What does the GeSHi plugin do?

GeSHi is a syntax highlighter for HTML, written in PHP. Basically, you input the source you want to highlight and the name of the language you want to highlight it in, and GeSHi returns the syntax-highlighted result.
(example in "sample.index.php")

The GeSHi class is already instanced in the "$geshi" variable, so you don't need to make another instance.

To use all the features that GeSHi has to offer, you may refer to its documentation in the following link: http://qbnz.com/highlighter/geshi-doc.html