Tips for parsing $this->EE->TMPL->tagdata?

I’m trying to parse $this->EE->TMPL->tagdata in this simple plugin I’m trying to build but I’m having a tough time. For instance, this returns FALSE:

strpos($this->EE->TMPL->tagdata, “<”);

This is an HTML string with a strlen() of 1600+ characters. Yet it can’t find an opening or closing bracket… very strange.

Is there a preferred way of parsing HTML strings with CI/EE?