Regex: Named groups/backreferences

Lars T Hansen lth at
Thu Sep 13 09:12:10 PDT 2007

On 9/13/07, liorean <liorean at> wrote:
> 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)?

The latter, but thanks for asking; I should clarify that in the spec.

> 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
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