Apply suggestions from code review

Co-authored-by: Addison Phillips <[email protected]>

Author: eemeli

exploration/0002-expression-attributes.md

@@ -8,7 +8,7 @@
 		<dt>First proposed</dt>
 		<dd>2023-08-27</dd>
 		<dt>Pull Request</dt>
-		<dd>#000</dd>
+		<dd><a href="https://github.com/unicode-org/message-format-wg/pull/458">#458</a></dd>
 	</dl>
 </details>
 
@@ -53,11 +53,13 @@ At least the following expression attributes should be considered:
 
 ## Requirements
 
-Attributes should be assignable to un-annotated expressions.
+Attributes can be assigned to any expression,
+including expressions without an annotation.
 
-Attributes should be distinct from function options.
+Attributes are distinct from function options.
 
-Common attributes should be definable by the specification.
+Common attributes are defined by the MF2 specification
+and must be supported by all implementations.
 
 Attributes should be user-definable.