Clarify guide for unbraced closures, regarding comments

Author: joshtriplett

guide/expressions.md

@@ -122,8 +122,8 @@ closure. Between the `|`s, you should use function definition syntax, however,
 elide types where possible.
 
 Use closures without the enclosing `{}`, if possible. Add the `{}` when you have
-a return type, when there are statements, when there are comments in the body,
-or when the body expression spans multiple lines and is a control-flow
+a return type, when there are statements, when there are comments inside the
+closure, or when the body expression spans multiple lines and is a control-flow
 expression. If using braces, follow the rules above for blocks. Examples:
 
 ```rust