minor: commit compatibility doc (#1358)

Leftover from #1349

Author: kazuyukitanimura

docs/source/user-guide/compatibility.md

@@ -32,12 +32,6 @@ be used in production.
 
 There is an [epic](https://github.com/apache/datafusion-comet/issues/313) where we are tracking the work to fully implement ANSI support.
 
-## Regular Expressions
-
-Comet uses the Rust regexp crate for evaluating regular expressions, and this has different behavior from Java's
-regular expression engine. Comet will fall back to Spark for patterns that are known to produce different results, but
-this can be overridden by setting `spark.comet.regexp.allowIncompatible=true`.
-
 ## Floating number comparison
 
 Spark normalizes NaN and zero for floating point numbers for several cases. See `NormalizeFloatingNumbers` optimization rule in Spark.
@@ -46,6 +40,22 @@ because they are handled well in Spark (e.g., `SQLOrderingUtil.compareFloats`).
 functions of arrow-rs used by DataFusion do not normalize NaN and zero (e.g., [arrow::compute::kernels::cmp::eq](https://docs.rs/arrow/latest/arrow/compute/kernels/cmp/fn.eq.html#)).
 So Comet will add additional normalization expression of NaN and zero for comparison.
 
+## Incompatible Expressions
+
+Some Comet native expressions are not 100% compatible with Spark and are disabled by default. These expressions
+will fall back to Spark but can be enabled by setting `spark.comet.expression.allowIncompatible=true`.
+
+## Array Expressions
+
+Comet has experimental support for a number of array expressions. These are experimental and currently marked
+as incompatible and can be enabled by setting `spark.comet.expression.allowIncompatible=true`.
+
+## Regular Expressions
+
+Comet uses the Rust regexp crate for evaluating regular expressions, and this has different behavior from Java's
+regular expression engine. Comet will fall back to Spark for patterns that are known to produce different results, but
+this can be overridden by setting `spark.comet.regexp.allowIncompatible=true`.
+
 ## Cast
 
 Cast operations in Comet fall into three levels of support: