2.1.19 [ECMA-262/9:2018] Section 14.1.2 Static Semantics: Early Errors

V0063: The LexicallyDeclaredNames of FunctionStatementList may have duplicate function and generator function entries

The specification states:

 14.1.2 Static Semantics: Early Errors
     ...
     FunctionBody : FunctionStatementList
  
         • It is a Syntax Error if the LexicallyDeclaredNames of FunctionStatementList 
         contains any duplicate entries.
         • It is a Syntax Error if any element of the LexicallyDeclaredNames of 
         FunctionStatementList also occurs in the VarDeclaredNames of 
         FunctionStatementList.
         • It is a Syntax Error if ContainsDuplicateLabels of FunctionStatementList with 
         argument « » is true.
         • It is a Syntax Error if ContainsUndefinedBreakTarget of FunctionStatementList 
         with argument « » is true.
         • It is a Syntax Error if ContainsUndefinedContinueTarget of 
         FunctionStatementList with arguments « » and « » is true.

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The LexicallyDeclaredNames of FunctionStatementList may have duplicate function and generator function entries.