What's (in) a module?

[Thomas A.Schmitz <thomas.schmitz@uni-bonn.de>]

Two maybe related questions:

1. What constitutes a module? I wrote a couple of definitions and put 
them in a file t-foo.tex. When I write "\input t-foo" in the preamble 
of my document, everything works fine (so the file is found by TeX). 
When I say \usemodule[t-foo] or \usemodule[foo], I get "system          
: no macros found in module foo" and, obviously, "undefined control 
sequence." So: is there any special form for a module? I'm very curious 
because I defined a set of similar macros in another module, and 
everything works fine.

2. Is it possible to use a certain encoding file, enco-bar.tex, for 
parts of a file only? Could one define a macro (in a module???) that 
would do something like \switchtoencoding[bar] and switch back to the 
file's default encoding afterwards?

Thanks to all, best

Thomas