<substitution oldstring=".PP .sp" newstring=".PP"/>
<!-- * squeeze multiple newlines after start of no-fill (verbatim) env. -->
<substitution oldstring=".nf " newstring=".nf "/>
+ <!-- * squeeze multiple newlines after REstoring margin -->
+ <substitution oldstring=".RE " newstring=".RE "/>
<!-- * an apostrophe at the beginning of a line gets interpreted as a -->
<!-- * roff request (groff(7) says it is "the non-breaking control -->
<!-- * character"); so we must add backslash before any apostrophe -->