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:
full parameter display for user defined functions
function name, file name and line indications
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