How to include files in plugins

[furrykef]

I'm writing a plugin that changes certain keywords into links. What I'm doing is I'm adding a hook at postbit_display_complete, which I understand to be the part of the code that gets called after BBcode parsing is complete. I need to ensure that I don't do keywords substitution in inappropriate places, so I need to be able to parse the HTML.

So the logical thing would seem to be to include includes/class_xml.php and use the parser in there. The problem is I'm not sure how I should do the inclusion, since, as I'm doing it from a hook, it would be basically executed in the middle of a function. What should I do to make sure I include the file safely and correctly?

EDIT: Is adding

require_once(CWD . '/includes/class_xml.php');

under the global_start hook is the right way?

[s]EDIT #2: It's clear that the vB_XML_Parser class is not what I want, so the point is partially moot. I'd still like to know if this is the best way to include files, though. And if anybody has any recommendations on how to parse HTML, that'd be great.[/s] (Never mind, I've found a probable solution, discussed below.)

- Kef