It could be argued that the way to implement "enhanced" strings, eg strings with embedded attributes (html, rtf,....) is for someone to write a specific SV class to deal with that kind of string. As has been pointed out, a difficulty with this is that standard regexes must be able to operate on that SV, leading to all sorts of problems related to the extraction of the string representation, and the definition of the semantics of matching and substituting on that string. One way round this is to leave the semantics to implementor of the SV type. This could be done by having vtable methods for *all* string ops known to Perl; in particular m//, s// and tr//. The way this could work is for the Perl core to provide a generic regex library, which uses only the public interface to SVs to extract and manipulate its contents. Standard string SVs would have the relevant vtable entries point to these generic regex functions. However, if someone wants to implement a HTML SV type say, then (if they are keen enough) they can write their own m//, s// methods which are efficent (becuase they can access the internal representation), and can have whatever semantics the author wishes. However, since the internals of regexes are a dark art to me, I dont know whether is is sensible to have a single regex compiler, but multiple regex executors (if that's the right terminology).
