The documentation that comes with the Tcl and Tk distributions is commonly referred to as the man pages or as reference documentation. The form of this documentations is a generally brief page describing a particular command, its arguments, and a description of what the command does.
The format of the pages is a text markup language frequently referred to as *roff man - shorthand for nroff/troff and manual macro set. It is one of the most common formats on Unix-like systems for documenting the basic invocation and argument options for a program or a command within a program.
Among the ways to access "the manual pages" are
Translated manual pages
The fundamental "charter" manpage is of course called Tcl (nickname "Endekalogue"). The Wiki Endekalogue page lists translations (of the Tcl reference page) to more languages.
When writing documentation, a developer has to decide in what form to provide the documentation. There are various tools available to assist in this.
There is a tool called txt2man (see http://freshmeat.net/projects/txt2man/ ) which is said to convert plain ASCII text into man page format.
There are Tcl specific tools, such as dtp/doctools software, which provides the ability to write doc in a general form, then to generate various file formats for display purposes.
see also manpages
For instance, TMML and dtp are two tools designed to help Tcl developers document Tcl extensions and applications.