Comments in PHP can be used for several purposes, a very interesting one being that you can generate API documentation directly from them by using PHPDocumentor (http://www.phpdoc.org/).

Therefor one has to use a JavaDoc-like comment syntax (conforms to the DocBook DTD), example:

* in your development cycle save you a lot of time by preventing you having to rewrite

* major documentation parts to generate some usable form of documentation.
*/
?>
Some basic html-like formatting is supported with this (ie 
 tags) to create something of a layout.