Fixed variable expression text

Author: darrelmiller

versions/3.0.md

@@ -1737,7 +1737,7 @@ This object can be extended with [Specification Extensions](#specificationExtens
 
 ##### Key Expression
 
-The key used to identify the [Path Item Object](#pathItemObject) is a variable expression that can be evaluated in the context of a runtime HTTP request/response to identify the URL to be used for the callback request.
+The key used to identify the [Path Item Object](#pathItemObject) is a [runtime expression](#runtimeExpression) that can be evaluated in the context of a runtime HTTP request/response to identify the URL to be used for the callback request.
 A simple example might be `$request.body#/url`.
 However, using a [runtime expression](#runtimeExpression) the complete HTTP message can be accessed.
 This includes accessing any part of a body that can be accessed using a JSON Pointer [RFC6901](https://tools.ietf.org/html/rfc6901).