spell(1) collects words from the named documents and looks them up in a
spelling list. Words that neither occur among nor are derivable
(by applying certain inflections, prefixes or suffixes) from words in the
spelling list are printed on the standard output.

deroff(1) reads each file in sequence and removes all roff command lines,
backslash constructions, macro definitions, eqn constructs (between ".EQ"
and ".EN" lines or between delimiters), pic pictures, and table descriptions
and writes the remainder to the standard output.