Hyper-Text Markup Language is the proper term for HTML, and it is the language of home pages. You can always get a book on HTML as there are many, but since this is the information super-highway, and also the world wide web, click here for one website related to HTML and other internet information. You can also do a search for information with one of the many Internet search engines. It's also a good language for many system management tasks. Expression syntax corresponds quite closely to C expression syntax.
Recursion is of unlimited depth.
And the hash tables used by associative arrays grow as necessary to prevent degraded performance. Perl uses sophisticated pattern matching techniques to scan large amounts of data very quickly. Setuid Perl scripts are safer than C programs through a dataflow tracing mechanism which prevents many stupid security holes. If you have a problem that would ordinarily use sed or awk or sh, but it exceeds their capabilities or must run a little faster, and you don't want to write the silly thing in C, then Perl may be for you. There are also translators to turn your sed and awk scripts into Perl scripts.