Only com- mands at or below this nesting level will be traced. See below for sequence. From now on, proc will be invoked before Tcl calls command proce- dures to process commands in interp . There may be many traces in effect simultaneously for the same command interpreter. Data 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 com- mand, 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 substi- tution, 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.