The Xdebug extension helps you debugging your script by providing a lot of
valuable debug information. The debug information that Xdebug can provide
includes the following:

    * stack and function traces in error messages with:
          o full parameter display for user defined functions
          o function name, file name and line indications
          o support for member functions
    * memory allocation
    * protection for infinite recursions

Xdebug also provides:

    * profiling information for PHP scripts
    * script execution analysis
    * capabilities to debug your scripts interactively with a debug client

WWW: http://www.xdebug.org/