physics_constraints
physics_constraints is a console command available in all 
Source games. It highlights physics constraints in the map with colorful boxes. It will show data about the constraint entities involved in a debug overlay like that of ent_text. Syntax: physics_constraints <classname>/<targetname>. No argument picks what player is looking at.
Note:The game must be in Developer mode for this command to work properly.Without developer mode enabled, the command will only at best print information of the physics constraints to the console.
