So the definition of pattern is:

6.3.3. pattern

The value of this keyword MUST be a string. This string SHOULD be a valid regular expression, according to the ECMA-262 regular expression dialect.
A string instance is considered valid if the regular expression matches the instance successfully. Recall: regular expressions are not implicitly anchored.

Does that include the regex literal delimiter / which means that pattern values must look like /pattern/flags (ECMA-262 15.10 or 7.85) or does it just include the pattern (ECMA-262 15.10.1)?
The spec is unclear because it does not link to a specific section of ECMA-262
Can this be clarified? What is allowed? What is required?