--- man.1.original	2018-06-01 21:48:50.986316000 +0900
+++ man.1	2018-06-02 11:08:46.095097000 +0900
@@ -311,6 +311,24 @@
 the standard search path is inserted between the colons.
 If none of these conditions are met, it overrides the
 standard search path.
+.It Ev MANPROC
+.Xr man 1
+usually uses
+.Xr mandoc 1
+to format text inside it,
+but if there is a problem with the formatting behavior of mandoc, specify
+.Dq Li "groff"
+for MANPROC Be sure to change the behavior to use
+.Xr groff 1
+for fomatting text.
+.It Ev MANROFFOPT
+If
+.Xr groff 1
+is used internally, this variable is passed as options to groff, for example
+.Dq Li "-mja"
+,
+.Dq Li "-mfr"
+etc can be used.
 .It Ev MANROFFSEQ
 Used to determine the preprocessors for the manual source before running
 .Xr nroff 1