If you require etags.fs, a new TAGS file will be
produced (see Tags Tables in Emacs Manual) that
contains the definitions of all words defined afterwards. You can then
find the source for a word using M-.. Note that Emacs can use
several tags files at the same time (e.g., one for the Gforth sources
and one for your program, see Selecting a Tags
Table in Emacs Manual). The TAGS file for the preloaded words is
$(datadir)/gforth/$(VERSION)/TAGS (e.g.,
/usr/local/share/gforth/0.2.0/TAGS). To get the best behaviour
with etags.fs, you should avoid putting definitions both before
and after require etc., otherwise you will see the same file
visited several times by commands like tags-search.