Only commands at or below this nesting level will be traced. See below for details on the calling sequence. From now on, proc will be invoked before Tcl calls command procedures to process commands in interp . There may be many traces in effect simultaneously for the same command interpreter. ClientData typically points to an application-specific data structure that describes what to do when proc is invoked.
Command points to a string containing the text of the command, before any argument substitution.
Argc and argv give the final argument information that will be passed to cmdProc , after command, variable, and backslash substitution. Proc must not modify the command or argv strings. This occurs after argument parsing and substitution, so tracing for substituted commands occurs before tracing of the commands containing the substitutions. If there is a syntax error in a command, or if there is no command procedure associated with a command name, then no tracing will occur for that command.