[Version 14.0] Feature support for extension members

standard/attributes.md

@@ -905,7 +905,7 @@
 
 The attribute `CallerArgumentExpressionAttribute` is applied to a *target parameter*, and can result in the capture of the source-code text of a sibling parameter’s argument as a string, referred to here as the *captured string*.
 
-Except when it is the first parameter in an extension method, the target parameter shall have a *default_argument*. When applied to the first parameter of an extension method, the captured string is the source text of the receiver expression in an extension method invocation. If the method is invoked using static method syntax, the captured string is the argument corresponding to the first parameter.
+Except when it is the first parameter, which is not also an *extension_receiver_parameter* (§Extension-Members), in an extension method, the target parameter shall have a *default_argument*. When applied to the first parameter of an extension method, the captured string is the source text of the receiver expression in an extension method invocation. If the method is invoked using static method syntax, the captured string is the argument corresponding to the first parameter.
 
 Consider the following method declaration:
 

standard/basic-concepts.md

@@ -37,6 +37,7 @@ A method qualifies as a canditate entry point by satisfying the following requir
 - If the `async` modifier is present, the method’s return type shall be `System.Threading.Tasks.Task` or `System.Threading.Tasks.Task<int>`.
 - It shall not be an optional partial method ([§15.6.9.2](classes.md#15692-optional-partial-methods)) without an implementing declaration.
 - The parameter list shall either be empty, or have a single value parameter of type `string[]`.
+- It shall not be an extension method ([§15.6.10](classes.md#15610-extension-methods) and §Extension-members).
 
 The declared accessibility ([§7.4.2](basic-concepts.md#742-declared-accessibility)) of a method is ignored for the purposes of qualifying as a candidate entry point. At application startup the selected entry point is invoked regardless of its declared accessibility. However any declared accessibility continues to apply if the selected candidate entry point is invoked after application startup.