[replace this comment with more details on this tcllib module]
The module and its packages are a Tcllib'ification of CMcC's mime type recognition in pure tcl.
makr (2009-11-19) notes that the manual page is currently available at: http://tcllib.sourceforge.net/doc/filetypes.html
Have a look at tmag for an extension that is using libmagic directly.
Nicko : A simple command line tool and portable library to identify popular file types. Compiles as a command-line program or loadable Tcl module.