diff --git a/examples/compiled/bar_grouped_errorbar.vg.json b/examples/compiled/bar_grouped_errorbar.vg.json
index 1e6a3ac463..592c784ac6 100644
--- a/examples/compiled/bar_grouped_errorbar.vg.json
+++ b/examples/compiled/bar_grouped_errorbar.vg.json
@@ -30,12 +30,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_Acceleration\"] + datum[\"extent_Acceleration\"]",
+          "expr": "datum['center_Acceleration'] + datum['extent_Acceleration']",
           "as": "upper_Acceleration"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Acceleration\"] - datum[\"extent_Acceleration\"]",
+          "expr": "datum['center_Acceleration'] - datum['extent_Acceleration']",
           "as": "lower_Acceleration"
         },
         {
diff --git a/examples/compiled/boxplot_1D_horizontal.vg.json b/examples/compiled/boxplot_1D_horizontal.vg.json
index 717f0f259f..92556c6639 100644
--- a/examples/compiled/boxplot_1D_horizontal.vg.json
+++ b/examples/compiled/boxplot_1D_horizontal.vg.json
@@ -31,7 +31,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -45,7 +45,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_1D_horizontal_custom_mark.vg.json b/examples/compiled/boxplot_1D_horizontal_custom_mark.vg.json
index 776537f73c..6709a39636 100644
--- a/examples/compiled/boxplot_1D_horizontal_custom_mark.vg.json
+++ b/examples/compiled/boxplot_1D_horizontal_custom_mark.vg.json
@@ -31,7 +31,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -45,7 +45,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_1D_horizontal_explicit.vg.json b/examples/compiled/boxplot_1D_horizontal_explicit.vg.json
index 717f0f259f..92556c6639 100644
--- a/examples/compiled/boxplot_1D_horizontal_explicit.vg.json
+++ b/examples/compiled/boxplot_1D_horizontal_explicit.vg.json
@@ -31,7 +31,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -45,7 +45,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_1D_invalid.vg.json b/examples/compiled/boxplot_1D_invalid.vg.json
index ff84dca834..fe54f15cb5 100644
--- a/examples/compiled/boxplot_1D_invalid.vg.json
+++ b/examples/compiled/boxplot_1D_invalid.vg.json
@@ -36,7 +36,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "filter",
@@ -50,7 +50,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_1D_vertical.vg.json b/examples/compiled/boxplot_1D_vertical.vg.json
index ae064d4290..5d4fbd5778 100644
--- a/examples/compiled/boxplot_1D_vertical.vg.json
+++ b/examples/compiled/boxplot_1D_vertical.vg.json
@@ -31,7 +31,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -45,7 +45,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_2D_horizontal.vg.json b/examples/compiled/boxplot_2D_horizontal.vg.json
index eddb366808..64d44c2540 100644
--- a/examples/compiled/boxplot_2D_horizontal.vg.json
+++ b/examples/compiled/boxplot_2D_horizontal.vg.json
@@ -30,7 +30,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -44,7 +44,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_2D_horizontal_color_size.vg.json b/examples/compiled/boxplot_2D_horizontal_color_size.vg.json
index 9b69f67750..e3f9889449 100644
--- a/examples/compiled/boxplot_2D_horizontal_color_size.vg.json
+++ b/examples/compiled/boxplot_2D_horizontal_color_size.vg.json
@@ -30,7 +30,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -44,7 +44,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_2D_vertical.vg.json b/examples/compiled/boxplot_2D_vertical.vg.json
index c3e870d09d..7476612122 100644
--- a/examples/compiled/boxplot_2D_vertical.vg.json
+++ b/examples/compiled/boxplot_2D_vertical.vg.json
@@ -30,7 +30,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -44,7 +44,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_2D_vertical_single_per_group.vg.json b/examples/compiled/boxplot_2D_vertical_single_per_group.vg.json
index aaf6d6723e..b2bcb83a82 100644
--- a/examples/compiled/boxplot_2D_vertical_single_per_group.vg.json
+++ b/examples/compiled/boxplot_2D_vertical_single_per_group.vg.json
@@ -29,7 +29,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "filter",
@@ -43,7 +43,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_2D_vertical_single_per_group_color.vg.json b/examples/compiled/boxplot_2D_vertical_single_per_group_color.vg.json
index 3d46d99a2e..809c7835c2 100644
--- a/examples/compiled/boxplot_2D_vertical_single_per_group_color.vg.json
+++ b/examples/compiled/boxplot_2D_vertical_single_per_group_color.vg.json
@@ -29,7 +29,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "filter",
@@ -43,7 +43,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+          "expr": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_groupped.vg.json b/examples/compiled/boxplot_groupped.vg.json
index 258c7b6518..57694094f2 100644
--- a/examples/compiled/boxplot_groupped.vg.json
+++ b/examples/compiled/boxplot_groupped.vg.json
@@ -26,7 +26,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Acceleration\"] < datum[\"lower_box_Acceleration\"] - 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"])) || (datum[\"Acceleration\"] > datum[\"upper_box_Acceleration\"] + 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]))"
+          "expr": "(datum['Acceleration'] < datum['lower_box_Acceleration'] - 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration'])) || (datum['Acceleration'] > datum['upper_box_Acceleration'] + 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']))"
         },
         {
           "type": "filter",
@@ -40,7 +40,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Acceleration\"] - 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]) <= datum[\"Acceleration\"]) && (datum[\"Acceleration\"] <= datum[\"upper_box_Acceleration\"] + 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]))"
+          "expr": "(datum['lower_box_Acceleration'] - 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']) <= datum['Acceleration']) && (datum['Acceleration'] <= datum['upper_box_Acceleration'] + 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_tooltip_aggregate.vg.json b/examples/compiled/boxplot_tooltip_aggregate.vg.json
index 21dbd804b4..8875b7816a 100644
--- a/examples/compiled/boxplot_tooltip_aggregate.vg.json
+++ b/examples/compiled/boxplot_tooltip_aggregate.vg.json
@@ -30,7 +30,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -44,7 +44,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/boxplot_tooltip_not_aggregate.vg.json b/examples/compiled/boxplot_tooltip_not_aggregate.vg.json
index 8c5512a3ba..20fcc36827 100644
--- a/examples/compiled/boxplot_tooltip_not_aggregate.vg.json
+++ b/examples/compiled/boxplot_tooltip_not_aggregate.vg.json
@@ -30,7 +30,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "filter",
@@ -44,7 +44,7 @@
       "transform": [
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+          "expr": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/errorband_tooltip.vg.json b/examples/compiled/errorband_tooltip.vg.json
index 5dc465efe4..ba493645e7 100644
--- a/examples/compiled/errorband_tooltip.vg.json
+++ b/examples/compiled/errorband_tooltip.vg.json
@@ -26,12 +26,12 @@
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
           "as": "upper_Miles_per_Gallon"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
           "as": "lower_Miles_per_Gallon"
         }
       ]
diff --git a/examples/compiled/errorbar_tooltip.vg.json b/examples/compiled/errorbar_tooltip.vg.json
index 21572cd9cd..5f8391407b 100644
--- a/examples/compiled/errorbar_tooltip.vg.json
+++ b/examples/compiled/errorbar_tooltip.vg.json
@@ -19,12 +19,12 @@
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_boxplot_circle.vg.json b/examples/compiled/layer_boxplot_circle.vg.json
index 96d93c3eb2..796231577c 100644
--- a/examples/compiled/layer_boxplot_circle.vg.json
+++ b/examples/compiled/layer_boxplot_circle.vg.json
@@ -24,7 +24,7 @@
         },
         {
           "type": "filter",
-          "expr": "(datum[\"lower_box_people\"] - 1.5 * (datum[\"upper_box_people\"] - datum[\"lower_box_people\"]) <= datum[\"people\"]) && (datum[\"people\"] <= datum[\"upper_box_people\"] + 1.5 * (datum[\"upper_box_people\"] - datum[\"lower_box_people\"]))"
+          "expr": "(datum['lower_box_people'] - 1.5 * (datum['upper_box_people'] - datum['lower_box_people']) <= datum['people']) && (datum['people'] <= datum['upper_box_people'] + 1.5 * (datum['upper_box_people'] - datum['lower_box_people']))"
         },
         {
           "type": "aggregate",
diff --git a/examples/compiled/layer_line_errorband_pre_aggregated.vg.json b/examples/compiled/layer_line_errorband_pre_aggregated.vg.json
index ec42299e65..1f723da821 100644
--- a/examples/compiled/layer_line_errorband_pre_aggregated.vg.json
+++ b/examples/compiled/layer_line_errorband_pre_aggregated.vg.json
@@ -52,8 +52,8 @@
       "name": "data_1",
       "source": "data_0",
       "transform": [
-        {"type": "formula", "expr": "datum[\"ci0\"]", "as": "upper_ci1"},
-        {"type": "formula", "expr": "datum[\"ci1\"]", "as": "lower_ci1"}
+        {"type": "formula", "expr": "datum['ci0']", "as": "upper_ci1"},
+        {"type": "formula", "expr": "datum['ci1']", "as": "lower_ci1"}
       ]
     }
   ],
diff --git a/examples/compiled/layer_point_errorbar_1d_horizontal.vg.json b/examples/compiled/layer_point_errorbar_1d_horizontal.vg.json
index 306057e4fd..d4cde6a165 100644
--- a/examples/compiled/layer_point_errorbar_1d_horizontal.vg.json
+++ b/examples/compiled/layer_point_errorbar_1d_horizontal.vg.json
@@ -36,12 +36,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_1d_vertical.vg.json b/examples/compiled/layer_point_errorbar_1d_vertical.vg.json
index 50011daa62..1f61c232a4 100644
--- a/examples/compiled/layer_point_errorbar_1d_vertical.vg.json
+++ b/examples/compiled/layer_point_errorbar_1d_vertical.vg.json
@@ -36,12 +36,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_2d_horizontal.vg.json b/examples/compiled/layer_point_errorbar_2d_horizontal.vg.json
index 672ec33639..15f59a9775 100644
--- a/examples/compiled/layer_point_errorbar_2d_horizontal.vg.json
+++ b/examples/compiled/layer_point_errorbar_2d_horizontal.vg.json
@@ -35,12 +35,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_2d_horizontal_color_encoding.vg.json b/examples/compiled/layer_point_errorbar_2d_horizontal_color_encoding.vg.json
index 443e0c3f29..4a4a129f46 100644
--- a/examples/compiled/layer_point_errorbar_2d_horizontal_color_encoding.vg.json
+++ b/examples/compiled/layer_point_errorbar_2d_horizontal_color_encoding.vg.json
@@ -35,12 +35,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ]
diff --git a/examples/compiled/layer_point_errorbar_2d_horizontal_custom_ticks.vg.json b/examples/compiled/layer_point_errorbar_2d_horizontal_custom_ticks.vg.json
index 77a39ccee1..01b801afca 100644
--- a/examples/compiled/layer_point_errorbar_2d_horizontal_custom_ticks.vg.json
+++ b/examples/compiled/layer_point_errorbar_2d_horizontal_custom_ticks.vg.json
@@ -35,12 +35,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ]
diff --git a/examples/compiled/layer_point_errorbar_2d_horizontal_stdev.vg.json b/examples/compiled/layer_point_errorbar_2d_horizontal_stdev.vg.json
index 76ec714e4b..9c7584b42e 100644
--- a/examples/compiled/layer_point_errorbar_2d_horizontal_stdev.vg.json
+++ b/examples/compiled/layer_point_errorbar_2d_horizontal_stdev.vg.json
@@ -35,12 +35,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_2d_vertical.vg.json b/examples/compiled/layer_point_errorbar_2d_vertical.vg.json
index 40ebf0cb7b..cd3e8daaed 100644
--- a/examples/compiled/layer_point_errorbar_2d_vertical.vg.json
+++ b/examples/compiled/layer_point_errorbar_2d_vertical.vg.json
@@ -35,12 +35,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_pre_aggregated_asymmetric_error.vg.json b/examples/compiled/layer_point_errorbar_pre_aggregated_asymmetric_error.vg.json
index c4920cf063..a622087510 100644
--- a/examples/compiled/layer_point_errorbar_pre_aggregated_asymmetric_error.vg.json
+++ b/examples/compiled/layer_point_errorbar_pre_aggregated_asymmetric_error.vg.json
@@ -40,12 +40,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"yield_center\"] + datum[\"yield_error\"]",
+          "expr": "datum['yield_center'] + datum['yield_error']",
           "as": "upper_yield_center"
         },
         {
           "type": "formula",
-          "expr": "datum[\"yield_center\"] + datum[\"yield_error2\"]",
+          "expr": "datum['yield_center'] + datum['yield_error2']",
           "as": "lower_yield_center"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_pre_aggregated_symmetric_error.vg.json b/examples/compiled/layer_point_errorbar_pre_aggregated_symmetric_error.vg.json
index 05fc1ffb53..44d400cca8 100644
--- a/examples/compiled/layer_point_errorbar_pre_aggregated_symmetric_error.vg.json
+++ b/examples/compiled/layer_point_errorbar_pre_aggregated_symmetric_error.vg.json
@@ -28,12 +28,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"yield_center\"] + datum[\"yield_error\"]",
+          "expr": "datum['yield_center'] + datum['yield_error']",
           "as": "upper_yield_center"
         },
         {
           "type": "formula",
-          "expr": "datum[\"yield_center\"] - datum[\"yield_error\"]",
+          "expr": "datum['yield_center'] - datum['yield_error']",
           "as": "lower_yield_center"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_pre_aggregated_upper_lower.vg.json b/examples/compiled/layer_point_errorbar_pre_aggregated_upper_lower.vg.json
index 7ee0833181..1f959353dc 100644
--- a/examples/compiled/layer_point_errorbar_pre_aggregated_upper_lower.vg.json
+++ b/examples/compiled/layer_point_errorbar_pre_aggregated_upper_lower.vg.json
@@ -40,12 +40,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"lower_yield\"]",
+          "expr": "datum['lower_yield']",
           "as": "upper_upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"upper_yield\"]",
+          "expr": "datum['upper_yield']",
           "as": "lower_upper_yield"
         },
         {
diff --git a/examples/compiled/layer_point_errorbar_stdev.vg.json b/examples/compiled/layer_point_errorbar_stdev.vg.json
index a94650dfa7..48d896eaf1 100644
--- a/examples/compiled/layer_point_errorbar_stdev.vg.json
+++ b/examples/compiled/layer_point_errorbar_stdev.vg.json
@@ -25,12 +25,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "expr": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         },
         {
diff --git a/examples/compiled/layer_scatter_errorband_1D_stdev_global_mean.vg.json b/examples/compiled/layer_scatter_errorband_1D_stdev_global_mean.vg.json
index bc686f03d5..a5ca1aeb47 100644
--- a/examples/compiled/layer_scatter_errorband_1D_stdev_global_mean.vg.json
+++ b/examples/compiled/layer_scatter_errorband_1D_stdev_global_mean.vg.json
@@ -55,12 +55,12 @@
       "transform": [
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
           "as": "upper_Miles_per_Gallon"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
           "as": "lower_Miles_per_Gallon"
         },
         {
diff --git a/examples/compiled/layer_scatter_errorband_1d_stdev.vg.json b/examples/compiled/layer_scatter_errorband_1d_stdev.vg.json
index e19f0d8252..f59f30fb20 100644
--- a/examples/compiled/layer_scatter_errorband_1d_stdev.vg.json
+++ b/examples/compiled/layer_scatter_errorband_1d_stdev.vg.json
@@ -30,12 +30,12 @@
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
           "as": "upper_Miles_per_Gallon"
         },
         {
           "type": "formula",
-          "expr": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+          "expr": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
           "as": "lower_Miles_per_Gallon"
         },
         {
diff --git a/examples/specs/normalized/bar_grouped_errorbar_normalized.vl.json b/examples/specs/normalized/bar_grouped_errorbar_normalized.vl.json
index 8cf5b30ec2..471acc54b9 100644
--- a/examples/specs/normalized/bar_grouped_errorbar_normalized.vl.json
+++ b/examples/specs/normalized/bar_grouped_errorbar_normalized.vl.json
@@ -30,11 +30,11 @@
           "groupby": ["Cylinders", "Origin"]
         },
         {
-          "calculate": "datum[\"center_Acceleration\"] + datum[\"extent_Acceleration\"]",
+          "calculate": "datum['center_Acceleration'] + datum['extent_Acceleration']",
           "as": "upper_Acceleration"
         },
         {
-          "calculate": "datum[\"center_Acceleration\"] - datum[\"extent_Acceleration\"]",
+          "calculate": "datum['center_Acceleration'] - datum['extent_Acceleration']",
           "as": "lower_Acceleration"
         }
       ],
diff --git a/examples/specs/normalized/boxplot_1D_horizontal_custom_mark_normalized.vl.json b/examples/specs/normalized/boxplot_1D_horizontal_custom_mark_normalized.vl.json
index fecd2fe25e..20878bf29d 100644
--- a/examples/specs/normalized/boxplot_1D_horizontal_custom_mark_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_1D_horizontal_custom_mark_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -41,7 +41,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_1D_horizontal_explicit_normalized.vl.json b/examples/specs/normalized/boxplot_1D_horizontal_explicit_normalized.vl.json
index 3346ac339f..78ff30b9e1 100644
--- a/examples/specs/normalized/boxplot_1D_horizontal_explicit_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_1D_horizontal_explicit_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -41,7 +41,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_1D_horizontal_normalized.vl.json b/examples/specs/normalized/boxplot_1D_horizontal_normalized.vl.json
index 3346ac339f..78ff30b9e1 100644
--- a/examples/specs/normalized/boxplot_1D_horizontal_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_1D_horizontal_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -41,7 +41,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_1D_invalid_normalized.vl.json b/examples/specs/normalized/boxplot_1D_invalid_normalized.vl.json
index dce2524e3d..10c7453cc5 100644
--- a/examples/specs/normalized/boxplot_1D_invalid_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_1D_invalid_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -41,7 +41,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_1D_vertical_normalized.vl.json b/examples/specs/normalized/boxplot_1D_vertical_normalized.vl.json
index 6a0640cc08..2e80baef15 100644
--- a/examples/specs/normalized/boxplot_1D_vertical_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_1D_vertical_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -41,7 +41,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_2D_horizontal_color_size_normalized.vl.json b/examples/specs/normalized/boxplot_2D_horizontal_color_size_normalized.vl.json
index e7c86be774..ff79852a44 100644
--- a/examples/specs/normalized/boxplot_2D_horizontal_color_size_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_2D_horizontal_color_size_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -43,7 +43,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_2D_horizontal_normalized.vl.json b/examples/specs/normalized/boxplot_2D_horizontal_normalized.vl.json
index ccd9dc76e3..48e677b3b8 100644
--- a/examples/specs/normalized/boxplot_2D_horizontal_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_2D_horizontal_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -42,7 +42,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_2D_vertical_normalized.vl.json b/examples/specs/normalized/boxplot_2D_vertical_normalized.vl.json
index 6acebbfc1b..608b1218bd 100644
--- a/examples/specs/normalized/boxplot_2D_vertical_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_2D_vertical_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -43,7 +43,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_2D_vertical_single_per_group_color_normalized.vl.json b/examples/specs/normalized/boxplot_2D_vertical_single_per_group_color_normalized.vl.json
index f33ab5ebd9..361caabf32 100644
--- a/examples/specs/normalized/boxplot_2D_vertical_single_per_group_color_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_2D_vertical_single_per_group_color_normalized.vl.json
@@ -19,7 +19,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -32,7 +32,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_2D_vertical_single_per_group_normalized.vl.json b/examples/specs/normalized/boxplot_2D_vertical_single_per_group_normalized.vl.json
index dc2969b67a..98086e3af3 100644
--- a/examples/specs/normalized/boxplot_2D_vertical_single_per_group_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_2D_vertical_single_per_group_normalized.vl.json
@@ -19,7 +19,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"b\"] < datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"])) || (datum[\"b\"] > datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['b'] < datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b'])) || (datum['b'] > datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -31,7 +31,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_b\"] - 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]) <= datum[\"b\"]) && (datum[\"b\"] <= datum[\"upper_box_b\"] + 1.5 * (datum[\"upper_box_b\"] - datum[\"lower_box_b\"]))"
+              "filter": "(datum['lower_box_b'] - 1.5 * (datum['upper_box_b'] - datum['lower_box_b']) <= datum['b']) && (datum['b'] <= datum['upper_box_b'] + 1.5 * (datum['upper_box_b'] - datum['lower_box_b']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_groupped_normalized.vl.json b/examples/specs/normalized/boxplot_groupped_normalized.vl.json
index 668b0f1257..49ca64b4c4 100644
--- a/examples/specs/normalized/boxplot_groupped_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_groupped_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Acceleration\"] < datum[\"lower_box_Acceleration\"] - 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"])) || (datum[\"Acceleration\"] > datum[\"upper_box_Acceleration\"] + 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]))"
+              "filter": "(datum['Acceleration'] < datum['lower_box_Acceleration'] - 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration'])) || (datum['Acceleration'] > datum['upper_box_Acceleration'] + 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -43,7 +43,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Acceleration\"] - 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]) <= datum[\"Acceleration\"]) && (datum[\"Acceleration\"] <= datum[\"upper_box_Acceleration\"] + 1.5 * (datum[\"upper_box_Acceleration\"] - datum[\"lower_box_Acceleration\"]))"
+              "filter": "(datum['lower_box_Acceleration'] - 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']) <= datum['Acceleration']) && (datum['Acceleration'] <= datum['upper_box_Acceleration'] + 1.5 * (datum['upper_box_Acceleration'] - datum['lower_box_Acceleration']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_tooltip_aggregate_normalized.vl.json b/examples/specs/normalized/boxplot_tooltip_aggregate_normalized.vl.json
index 3180a7c526..a0e818aa29 100644
--- a/examples/specs/normalized/boxplot_tooltip_aggregate_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_tooltip_aggregate_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -42,7 +42,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/boxplot_tooltip_not_aggregate_normalized.vl.json b/examples/specs/normalized/boxplot_tooltip_not_aggregate_normalized.vl.json
index e5259d3b63..263bfb9a8a 100644
--- a/examples/specs/normalized/boxplot_tooltip_not_aggregate_normalized.vl.json
+++ b/examples/specs/normalized/boxplot_tooltip_not_aggregate_normalized.vl.json
@@ -25,7 +25,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"Body Mass (g)\"] < datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"])) || (datum[\"Body Mass (g)\"] > datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['Body Mass (g)'] < datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)'])) || (datum['Body Mass (g)'] > datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             }
           ],
           "mark": {"type": "point", "style": "boxplot-outliers"},
@@ -43,7 +43,7 @@
         {
           "transform": [
             {
-              "filter": "(datum[\"lower_box_Body Mass (g)\"] - 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]) <= datum[\"Body Mass (g)\"]) && (datum[\"Body Mass (g)\"] <= datum[\"upper_box_Body Mass (g)\"] + 1.5 * (datum[\"upper_box_Body Mass (g)\"] - datum[\"lower_box_Body Mass (g)\"]))"
+              "filter": "(datum['lower_box_Body Mass (g)'] - 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']) <= datum['Body Mass (g)']) && (datum['Body Mass (g)'] <= datum['upper_box_Body Mass (g)'] + 1.5 * (datum['upper_box_Body Mass (g)'] - datum['lower_box_Body Mass (g)']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/errorband_tooltip_normalized.vl.json b/examples/specs/normalized/errorband_tooltip_normalized.vl.json
index c2fa37de1d..f1467540cc 100644
--- a/examples/specs/normalized/errorband_tooltip_normalized.vl.json
+++ b/examples/specs/normalized/errorband_tooltip_normalized.vl.json
@@ -19,11 +19,11 @@
       "groupby": ["year_Year", "Miles_per_Gallon"]
     },
     {
-      "calculate": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+      "calculate": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
       "as": "upper_Miles_per_Gallon"
     },
     {
-      "calculate": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+      "calculate": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
       "as": "lower_Miles_per_Gallon"
     }
   ],
diff --git a/examples/specs/normalized/errorbar_tooltip_normalized.vl.json b/examples/specs/normalized/errorbar_tooltip_normalized.vl.json
index 996a16f38a..4e83ecd3c1 100644
--- a/examples/specs/normalized/errorbar_tooltip_normalized.vl.json
+++ b/examples/specs/normalized/errorbar_tooltip_normalized.vl.json
@@ -10,11 +10,11 @@
       "groupby": ["variety", "variety"]
     },
     {
-      "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+      "calculate": "datum['center_yield'] + datum['extent_yield']",
       "as": "upper_yield"
     },
     {
-      "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+      "calculate": "datum['center_yield'] - datum['extent_yield']",
       "as": "lower_yield"
     }
   ],
diff --git a/examples/specs/normalized/layer_boxplot_circle_normalized.vl.json b/examples/specs/normalized/layer_boxplot_circle_normalized.vl.json
index 4b9038e964..441df1830f 100644
--- a/examples/specs/normalized/layer_boxplot_circle_normalized.vl.json
+++ b/examples/specs/normalized/layer_boxplot_circle_normalized.vl.json
@@ -16,7 +16,7 @@
               "groupby": ["age"]
             },
             {
-              "filter": "(datum[\"lower_box_people\"] - 1.5 * (datum[\"upper_box_people\"] - datum[\"lower_box_people\"]) <= datum[\"people\"]) && (datum[\"people\"] <= datum[\"upper_box_people\"] + 1.5 * (datum[\"upper_box_people\"] - datum[\"lower_box_people\"]))"
+              "filter": "(datum['lower_box_people'] - 1.5 * (datum['upper_box_people'] - datum['lower_box_people']) <= datum['people']) && (datum['people'] <= datum['upper_box_people'] + 1.5 * (datum['upper_box_people'] - datum['lower_box_people']))"
             },
             {
               "aggregate": [
diff --git a/examples/specs/normalized/layer_line_errorband_pre_aggregated_normalized.vl.json b/examples/specs/normalized/layer_line_errorband_pre_aggregated_normalized.vl.json
index 2080ffec81..27e45fcad8 100644
--- a/examples/specs/normalized/layer_line_errorband_pre_aggregated_normalized.vl.json
+++ b/examples/specs/normalized/layer_line_errorband_pre_aggregated_normalized.vl.json
@@ -12,8 +12,8 @@
     {
       "transform": [
         {"timeUnit": {"unit": "year"}, "field": "Year", "as": "year_Year"},
-        {"calculate": "datum[\"ci0\"]", "as": "upper_ci1"},
-        {"calculate": "datum[\"ci1\"]", "as": "lower_ci1"}
+        {"calculate": "datum['ci0']", "as": "upper_ci1"},
+        {"calculate": "datum['ci1']", "as": "lower_ci1"}
       ],
       "layer": [
         {
diff --git a/examples/specs/normalized/layer_point_errorbar_1d_horizontal_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_1d_horizontal_normalized.vl.json
index 266e618a9c..79a8db1cdd 100644
--- a/examples/specs/normalized/layer_point_errorbar_1d_horizontal_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_1d_horizontal_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": []
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_1d_vertical_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_1d_vertical_normalized.vl.json
index 6f264919e1..1b32e8e775 100644
--- a/examples/specs/normalized/layer_point_errorbar_1d_vertical_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_1d_vertical_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": []
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_color_encoding_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_color_encoding_normalized.vl.json
index 413741ed78..68e2ff4f35 100644
--- a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_color_encoding_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_color_encoding_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_custom_ticks_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_custom_ticks_normalized.vl.json
index 7796c08b99..b396742d7f 100644
--- a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_custom_ticks_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_custom_ticks_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_normalized.vl.json
index e7e82a6c8b..0b752657a1 100644
--- a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_stdev_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_stdev_normalized.vl.json
index 64d6a61ffb..d1545ba5c1 100644
--- a/examples/specs/normalized/layer_point_errorbar_2d_horizontal_stdev_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_2d_horizontal_stdev_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_2d_vertical_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_2d_vertical_normalized.vl.json
index 4bf3e2d533..6dd61c4f79 100644
--- a/examples/specs/normalized/layer_point_errorbar_2d_vertical_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_2d_vertical_normalized.vl.json
@@ -12,11 +12,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_asymmetric_error_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_asymmetric_error_normalized.vl.json
index acd94f8a26..8735611767 100644
--- a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_asymmetric_error_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_asymmetric_error_normalized.vl.json
@@ -32,11 +32,11 @@
     {
       "transform": [
         {
-          "calculate": "datum[\"yield_center\"] + datum[\"yield_error\"]",
+          "calculate": "datum['yield_center'] + datum['yield_error']",
           "as": "upper_yield_center"
         },
         {
-          "calculate": "datum[\"yield_center\"] + datum[\"yield_error2\"]",
+          "calculate": "datum['yield_center'] + datum['yield_error2']",
           "as": "lower_yield_center"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_symmetric_error_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_symmetric_error_normalized.vl.json
index fa14822061..e480976649 100644
--- a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_symmetric_error_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_symmetric_error_normalized.vl.json
@@ -12,11 +12,11 @@
     {
       "transform": [
         {
-          "calculate": "datum[\"yield_center\"] + datum[\"yield_error\"]",
+          "calculate": "datum['yield_center'] + datum['yield_error']",
           "as": "upper_yield_center"
         },
         {
-          "calculate": "datum[\"yield_center\"] - datum[\"yield_error\"]",
+          "calculate": "datum['yield_center'] - datum['yield_error']",
           "as": "lower_yield_center"
         }
       ],
diff --git a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_upper_lower_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_upper_lower_normalized.vl.json
index 7ca7d505c8..ddff34cb89 100644
--- a/examples/specs/normalized/layer_point_errorbar_pre_aggregated_upper_lower_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_pre_aggregated_upper_lower_normalized.vl.json
@@ -31,8 +31,8 @@
   "layer": [
     {
       "transform": [
-        {"calculate": "datum[\"lower_yield\"]", "as": "upper_upper_yield"},
-        {"calculate": "datum[\"upper_yield\"]", "as": "lower_upper_yield"}
+        {"calculate": "datum['lower_yield']", "as": "upper_upper_yield"},
+        {"calculate": "datum['upper_yield']", "as": "lower_upper_yield"}
       ],
       "mark": {
         "type": "rule",
diff --git a/examples/specs/normalized/layer_point_errorbar_stdev_normalized.vl.json b/examples/specs/normalized/layer_point_errorbar_stdev_normalized.vl.json
index b17ca84dad..15d232c9e6 100644
--- a/examples/specs/normalized/layer_point_errorbar_stdev_normalized.vl.json
+++ b/examples/specs/normalized/layer_point_errorbar_stdev_normalized.vl.json
@@ -26,11 +26,11 @@
           "groupby": ["variety"]
         },
         {
-          "calculate": "datum[\"center_yield\"] + datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] + datum['extent_yield']",
           "as": "upper_yield"
         },
         {
-          "calculate": "datum[\"center_yield\"] - datum[\"extent_yield\"]",
+          "calculate": "datum['center_yield'] - datum['extent_yield']",
           "as": "lower_yield"
         }
       ],
diff --git a/examples/specs/normalized/layer_scatter_errorband_1D_stdev_global_mean_normalized.vl.json b/examples/specs/normalized/layer_scatter_errorband_1D_stdev_global_mean_normalized.vl.json
index 67cb4323af..4e990e49ad 100644
--- a/examples/specs/normalized/layer_scatter_errorband_1D_stdev_global_mean_normalized.vl.json
+++ b/examples/specs/normalized/layer_scatter_errorband_1D_stdev_global_mean_normalized.vl.json
@@ -28,11 +28,11 @@
           "groupby": []
         },
         {
-          "calculate": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+          "calculate": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
           "as": "upper_Miles_per_Gallon"
         },
         {
-          "calculate": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+          "calculate": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
           "as": "lower_Miles_per_Gallon"
         }
       ],
diff --git a/examples/specs/normalized/layer_scatter_errorband_1d_stdev_normalized.vl.json b/examples/specs/normalized/layer_scatter_errorband_1d_stdev_normalized.vl.json
index a8d3ee6382..f4791a049c 100644
--- a/examples/specs/normalized/layer_scatter_errorband_1d_stdev_normalized.vl.json
+++ b/examples/specs/normalized/layer_scatter_errorband_1d_stdev_normalized.vl.json
@@ -27,11 +27,11 @@
           "groupby": []
         },
         {
-          "calculate": "datum[\"center_Miles_per_Gallon\"] + datum[\"extent_Miles_per_Gallon\"]",
+          "calculate": "datum['center_Miles_per_Gallon'] + datum['extent_Miles_per_Gallon']",
           "as": "upper_Miles_per_Gallon"
         },
         {
-          "calculate": "datum[\"center_Miles_per_Gallon\"] - datum[\"extent_Miles_per_Gallon\"]",
+          "calculate": "datum['center_Miles_per_Gallon'] - datum['extent_Miles_per_Gallon']",
           "as": "lower_Miles_per_Gallon"
         }
       ],