Valid output types (or debug modes) are as follows:

Value Description
all Enable output of all types listed in this table
calls Print out entrances and exits to most subroutines to enable quick tracing of crash locations
commands Trace execution of commands in command lists (e.g. filters) and print information on variable access paths
gl Debug OpenGL calls and graphics capabilities as best as is possible
parse Debug file-reading and argument parsing routines
typing Print (lots of) information regarding setting and matching of atom type descriptions
verbose Enable a little extra output (but not much)