2.1.39 [ECMA-ES2017] Section 21.2.1 Patterns

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V0078: If the contents of the braces in \u{...} is not a hexadecimal number, \u{...} is treated as a regular string

The specification states:

 21.2.1 Patterns
  
     The RegExp constructor applies the following grammar to the input pattern String. An 
     error occurs if the grammar cannot interpret the String as an expansion of Pattern.
  
     Syntax
         ...
         RegExpUnicodeEscapeSequence[U] ::
             [+U] u LeadSurrogate \u TrailSurrogate
             [+U] u LeadSurrogate
             [+U] u TrailSurrogate
             [+U] u NonSurrogate
             [~U] u Hex4Digits
             [+U] u{ HexDigits }

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If the contents of the braces in \u{...} is not a hexadecimal number, \u{...} is treated as a regular string, rather than a Unicode code point. For example, the following returns true but should throw a SyntaxError exception:

    /\u{pp}/u.exec('\\u{pp}')