+.It Cm delim
+This statement takes a string argument consisting of two bytes,
+to be used as the opening and closing delimiters for equations
+in the middle of text input lines.
+Conventionally, the dollar sign is used for both delimiters,
+as follows:
+.Bd -literal -offset indent
+\&.EQ
+delim $$
+\&.EN
+An equation like $sin pi = 0$ can now be entered
+in the middle of a text input line.
+.Ed
+.Pp
+The special statement
+.Cm delim off
+temporarily disables previously declared delimiters and
+.Cm delim on
+reenables them.