Just about anything is possible with regexes if you go far enough but take one look at the back pages of Jeffrey Friedl's "Mastering Regular Expressions" to see the horrifying 2 page regex that results from parsing plain old email addresses correctly.

You might be able to do what you want the way you're trying but I would suggest instead giving Parse::RecDescent a shot. Bit of a learning curve but the resulting code will be much easier to read, tweak, and reuse.

(update: switched ISBN to 2nd ed.)