highlight.php is a server-side syntax highlighter written in PHP that currently supports 185 languages. It's a port of highlight.js by Ivan Sagalaev that makes full use of the language and style definitions of the original JavaScript project.
The ability to encode and decode a certain set of characters called 'Html Entities' has existed since PHP4. Amongst the vast number of functions built into PHP, there are 4 nearly identical functions that are used to encode and decode html entities; despite their similarities, however, 2 of them do provide additional capabilities not available to the others.