Hyphenation is on by default.
.nhturns it off,
.hy modeturns it on.
The optional argument to .hy is a bitmap of additional restrictions on hyphenation:
.hy 0is the same as .nh, and
.hy 1is the same as .hy, it just turns unrestricted hyphenation on.
hyphenating a word
.hw wo-rd1 wo-rd2 ...specifies how to hyphenate ``word1,'' ``word2,'' etc. for a whopping total of 128 characters.
hyphenating one particular case
.hc cspecifies c as the ``hyphenation character.'' (Default is \%).
\% wordIf the hyphenation character occurs before a word, the word is not hyphenated.
wo\%rdIf the hyphenation character occurs in a word, the word should be hyphenated there and nowhere else.
\% is listed in the appendix as ``the default optional hyphenation character.'' It prints as octal 024 (^T). In our local system, .hc x succeeds in disabling \% as hyphenation character, but doesn't seem to enable x.