A quick word about the notation used to describe Tcl commands. In general, a description of a command is the name of the command followed by its arguments separated by spaces. An example is:

     set varName ?value?

which is a description of the Tcl set command, which takes a variable name varName and an optional argument, a value.

Optional arguments are enclosed in question mark, ?, pairs, as in the example.

A series of three dots ... represents repeated arguments. An example is a description of the unset command:

     unset varName ?varName varName ...?

which shows that the unset command has at least one compulsory argument varName but has any number of subsequent optional arguments.