2.4.1 Extensions to Declaration Binding Instantiation
Internet Explorer ECMAScript allows a FunctionDeclaration language syntactic element to appear anywhere that a Statement can appear. FunctionDeclaration items are processed during step 5 of the Declaration Binding Instantiation algorithm (which is defined by [ECMA-262/5], section 10.5). However, a FunctionDeclaration item that defines an event handler is excluded from the processing of step 5. Such a FunctionDeclaration item is evaluated when an ECMAScript SourceElement production is evaluated.