Version 3 of command

Richard Suchenwirth - Tcl is the Tool Command Language. Execution is done by splitting scripts into commands (by newline or semicolon). A command is a sequence of words, the first being the command name, the rest its arguments. (So far from Tcl syntax). A specialized mantra would say "everything is a command", even what other languages call "control strucutures" (if, while, for...) or "declarations" (global, proc, variable...).

All available command names at a given time (and namespace) are returned by

 info commands

They may have come from several sources:

C-implemented commands
Tcl-implemented procs, listed in info procs
Aliases for other commands, listed in interp aliases {}
Tk widgets use their pathname as command; you can test whether a string is a widget command with winfo exists $name
images also use their name as command name, listed in image names
OO systems like incr Tcl also use object names in the command position

To introspect commands in other than the current namespace, walk the tree with namespace children.