Regex: Named groups/backreferences

[liorean]

Hello!

Got some questions about named groups:

"Group names must be valid lexical identifiers, and each group name
must be defined only once within a regular expression."

1. Is this meant to indicate that regex add their own lexical scopes;
partake in the lexical scope of their containing function if any; that
the identifier must be unique within the regex and that that null,
true, false, this etc. that are reserved keywords cannot be used (i.e.
the Identifier construct); or just that they need to conform to the
identifier syntax but reserved keywords are allowed (i.e. the
IdentifierName construct)?

2. Can (?P=varname) refer to a lexical variable varname from a
containing scope, or just to groups within the regex itself?

3. If it can refer to a variable in a containing scope, what
constraints are put on the variable type, what conversions are made,
etc?
-- 
David "liorean" Andersson