Xdebug is a debugging and productivity extension for PHP

Xdebug and provides a range of features to improve the PHP development
experience.

Step Debugging
A way to step through your code in your IDE or editor while the script is
executing.

Improvements to PHP's error reporting
An improved var_dump() function, stack traces for Notices, Warnings, Errors
and Exceptions to highlight the code path to the error

Tracing
Writes every function call, with arguments and invocation location to disk.
Optionally also includes every variable assignment and return value for
each function.

Profiling
Allows you, with the help of visualisation tools, to analyse the
performance of your PHP application and find bottlenecks.

Code Coverage Analysis
To show which parts of your code base are executed when running unit tests
with PHP Unit.

+ Added new features:
- DBGP: Added error messages to returned errors (in most cases)

+ Added new functions:
- Added a function "xdebug_debug_zval" to debug zvals by printing its
refcounts and is_ref values.

= Changed features:
- xdebug_code_coverage_stop() will now clean up the code coverage array,
unless you specify FALSE as parameter.
- The proper Xdebug type is "hash" for associative arrays.
- Extended the code-coverage functionality by returning lines with
executable code on them, but where not executed with a count value of -1.

= Fixed bugs:
- DBGP: Make property_get and property_value finally work as they should,
including retrieving information from different depths then the most top
stack frame.
- DBGP: Fix eval'ed $varnames in property_get.
- DBGP: Support the -d option for property_get.
- Fixed the exit handler hook to use the new "5.1" way of handling it;
which fortunately also works with PHP 5.0.
- Fixed bug #102: Problems with configure for automake 1.8.
- Fixed bug #101: crash with set_exeception_handler() and uncatched exceptions.
- Fixed bug #99: unset variables return the name as a string with property_get.
- Fixed bug #98: 'longname' attribute not returned for unintialized
property in context_get request.
- Fixed bug #94: xdebug_sprintf misbehaves with x86_64/glibc-2.3.3
- Fixed bug #93: Crash in lookup_hostname on x86_64
- Fixed bug #92: xdebug_disable() doesn't disable the exception handler.
- Fixed bug #68: Summary not written when script ended with "exit()".