The Blizzard DebugTools appeared in Patch 3.2 and added a set of new slash commands to assist with addon development and UI tweaking. Inspired/derived from Iriel's DevTools addon.
Frame stack 
Edit
Description Edit
Displays information about the frames under the mouse cursor.
Usage Edit
/framestack [showhidden] /fstack [showhidden]
Arguments Edit
showhidden - if "true" then will also display information about hidden frames
See Also Edit
Event Trace Edit
Description Edit
The EventTrace command assists addon developers in figuring out what events fire in certain circumstances. For example, you may want to know what order events fire when you zone into a random dungeon instance or when loot drops.
UsageEdit
/eventtrace [command] /etrace [command]
Arguments Edit
start - enables event capturing to the EventTrace frame
stop - disables event capturing
number - captures the provided number of events and then stops
If no command is given the EventTrace frame visibility is toggled. The first time the frame is displayed, event tracing is automatically started.
See Also Edit
Dump Edit
Description Edit
Used to print variables or expression results to the chat frame.
Usage Edit
/dump expression
expression can be any valid lua expression that results in a value. So variable names, function calls, frames or tables can all be dumped.
