diff --git a/base/docs/helpdb/Base.jl b/base/docs/helpdb/Base.jl
index 7150347716b7a..858faaecce8aa 100644
--- a/base/docs/helpdb/Base.jl
+++ b/base/docs/helpdb/Base.jl
@@ -3058,14 +3058,6 @@ Return `true` if `A` is a subset of or equal to `S`.
 """
 issubset
 
-"""
-    stringmime(mime, x)
-
-Returns an `AbstractString` containing the representation of `x` in the requested `mime`
-type. This is similar to [`reprmime`](:func:`reprmime`) except that binary data is base64-encoded as an ASCII string.
-"""
-stringmime
-
 """
     zero(x)
 
diff --git a/base/expr.jl b/base/expr.jl
index 391ce27fe4a74..a947184158d3a 100644
--- a/base/expr.jl
+++ b/base/expr.jl
@@ -88,8 +88,9 @@ julia> macro m()
 julia> M.f()
 (1,2)
 ```
-With `@macroexpand` the expression expands where `@macroexpand` appears in the code (module `M`).
-With `macroexpand` the expressions expands in the current module where the code was finally called (REPL).
+With `@macroexpand` the expression expands where `@macroexpand` appears in the code (module
+`M` in the example). With `macroexpand` the expression expands in the current module where
+the code was finally called (REPL in the example).
 Note that when calling `macroexpand` or `@macroexpand` directly from the REPL, both of these contexts coincide, hence there is no difference.
 """
 macro macroexpand(code)
diff --git a/doc/stdlib/base.rst b/doc/stdlib/base.rst
index b2385c9ac1933..0df85b45071a6 100644
--- a/doc/stdlib/base.rst
+++ b/doc/stdlib/base.rst
@@ -832,7 +832,27 @@ Nullables
 
    .. Docstring generated from Julia source
 
-   Is the ``Nullable`` object ``x`` null, i.e. missing a value?
+   Return whether or not ``x`` is null for :obj:`Nullable` ``x``\ ; return ``false`` for all other ``x``\ .
+
+   .. doctest::
+
+       julia> x = Nullable(1, false)
+       Nullable{Int64}(1)
+
+       julia> isnull(x)
+       false
+
+       julia> x = Nullable(1, true)
+       Nullable{Int64}()
+
+       julia> isnull(x)
+       true
+
+       julia> x = 1
+       1
+
+       julia> isnull(x)
+       false
 
 System
 ------
@@ -1545,7 +1565,7 @@ Internals
        julia> M.f()
        (1,2)
 
-   With @macroexpand the expression expands where @macroexpand appears in the code (module M). With macroexpand the expressions expands in the current module where the code was finally called. Note that when calling macroexpand or @macroexpand directly from the REPL, both of these contexts coincide, hence there is no difference.
+   With ``@macroexpand`` the expression expands where ``@macroexpand`` appears in the code (module ``M`` in the example). With ``macroexpand`` the expression expands in the current module where the code was finally called (REPL in the example). Note that when calling ``macroexpand`` or ``@macroexpand`` directly from the REPL, both of these contexts coincide, hence there is no difference.
 
 .. function:: expand(x)
 
@@ -1620,4 +1640,3 @@ Internals
    .. Docstring generated from Julia source
 
    Compile the given function ``f`` for the argument tuple (of types) ``args``\ , but do not execute it.
-
diff --git a/doc/stdlib/io-network.rst b/doc/stdlib/io-network.rst
index e40f9281bec99..8f31c0228d727 100644
--- a/doc/stdlib/io-network.rst
+++ b/doc/stdlib/io-network.rst
@@ -839,7 +839,7 @@ stack with:
 
    .. Docstring generated from Julia source
 
-   Determine whether a MIME type is text data.
+   Determine whether a MIME type is text data. MIME types are assumed to be binary data except for a set of types known to be text data (possibly Unicode).
 
 Memory-mapped I/O
 -----------------