Reverse Engineering Tools?

What tool can help me understand a huge PHP sourcecode?
Thanks!

[netstavi]

1, DzSoft PHP Editor 2.0.0.1 - hxxp://www.dzsoft.com

ÞÛÛ DzSoft PHP Editor is a user-friendly tool for editing ÛÛÝ
ÛÛ and testing PHP scripts and HTML/XML pages. Being ÛÛ
Û²Û designed specifically for PHP development, it is Û²Û
Û±± comfortable both for beginners and experienced ±±Û
ÛÛ programmers. Has convenient one-click preview in ÛÛ
ÛÛ internal browser (with no web server required), quick ÛÛ
Þ² insert features and many other things you may need for ²Ý
± easy and productive PHP development. ±

2, PHP Expert Editor 3.2 - hxxp://www.ankord.com

ÞÛÛ PHP Expert Editor is an easy-to-use PHP IDE (Integrated ÛÛÝ
ÛÛ Development Environment) for Windows. This Editor ÛÛ
Û²Û specially designed for PHP-masters and has a nice Û²Û
Û±± features for beginners and professional programmers. PHP ±±Û
ÛÛ Expert Editor has internal HTTP-server and Debugger to ÛÛ
ÛÛ run, test and debug PHP scripts (you can use any ÛÛ
Þ² external HTTP-server also). The PHP Syntax Check, ²Ý
± internal browser, Code Explorer, File Explorer, FTP ±
± client, Project Explorer, Library Explorer, Code ±
Þ±Ý Templates, three modes of code highlighting (PHP & HTML, Þ±Ý
Û²² HTML only, PHP only), Java Script and CSS files ²²Û
ÛÛß highlighting, quick navigation in code, and much more. ßÛÛ