How to extract textual content from an SGML DTD using Perl?

Question

I'm looking into extracting all the content from a DTD using Perl, but I'm not sure which is the best way to go about it. I know there are modules for working with XML, but I'm not sure if there are any for this type of work with SGML or if I should try to create a regular expression for this work?

I'm new to SGML and Perl along with not having much experience with regex, except for very simple pattern matching.