The documentation for the [[rename]] command is available at http://purl.org/tcl/home/man/tcl8.3.2/TclCmd/rename.htm .

The [[rename]] command is most often used for [wrapping commands].  In other words, the programmer uses [[rename]] to hide another command -- so that a wrapper can be placed around the hidden command to change its behavior.  Examples of this important concept abound on the Wiki;
among the clearest are:
[DGP]: Be aware that if you `rename` a command into another
   * [Overloading widgets]
   * [Text variable for text widget]
   * [Forward compatibility]

[[Discuss examples.  Explain errorInfo subtleties (refer to live examples).
Explain "return [eval ::_$original_command \$first_argument $args]"
idiom.]]

[RS] Another frequent application for [rename] is to remove commands, by renaming them to the empty string:
 rename foo {}

[Tcl syntax help]
- [Arts and crafts of Tcl-Tk programming]
- [Category Command]