Tcl for Embedded Applications
Download the Tcl Manual in printable Adobe PDF format. (Get the Acrobat Reader)
Examine the principle Tiny Tcl documentation, which has been (somewhat imperfectly) converted to HTML from nroff "man" format. It's a straight port of the standard 6.7 docs.
Read about the BIOS extensions, the DOS extensions, and the DOS video extensions.
Read about the compile environment and the runtime environment.
Discover how to add application-specific support in Tcl by adding new commands in C.