Use ellipsis more idiomatically, favoring it over plurals, and including
it within instead of outside option brackets for clarity.

The construction:

foo bar [baz] ...

is ambiguous.  If I specify no "baz", can "bar"s be repeated?

Also say "argument" when we mean an option OR an operand.

Content:
* More carefully distinguish escape sequences from device control
  commands; the former are more general.
* The *roff `\X` escape sequence is a device control command, not a
  "special".  *roff already freights the latter term with enough meaning
  without hauling in TeX's use for it.
* The "ps:" or "pdf:" part of a device control command escape sequence
  parameter is the "tag", not the entire parameter.  It is a name
  spacing convention.
* Clarify operation of `xrev` device control command.

Style:
* Recast: all device control commands are "extensions"; there is no
  standard set.
* Convert mentions of (g)pic(1) and grops(1) to man page cross
  references.
* Set pic(1) command names in bold, not italics.
* Set "mom" macro package name in italics, not bold.
* Set "gropdf" in italics, not bold.
* Capitalize "PDF" in prose.
* Protect Perl's "localtime" function name from hyphenation.
* Hyphenate adjectival phrases.
* Hyphenate metasyntactic variable consistently with its introduction.
* Otherwise recast for (attempted) clarity and concision.

Markup:
* Use two empty requests where vertical space is expected.
* Annotate a mismatch in conventions between grotty(1) and gropdf(1).

Content:
* Introduce the concept of convenience macros earlier, then rely on it.
* Align terminology regarding page location traps with the rest of
  groff's documentation.
* Align header/footer terminology with the rest of groff's
  documentation.

Style:
* Tighten wording.
* Set macro call literals in bold.
* Use imperative voice more when describing device control commands.
* Present convenience macros _after_ full discussion of device control
  command behavior, not in the midst of it.
* Coalesce some single-sentence paragraphs into their predecessors.

Markup:
* Set file names in italics.
* Protect macro call literals from hyphenation.
* Use an empty request between sentences.
* Use two empty requests where vertical space is expected.

The page references it several times; we should explain what it is and
link to it.

Drop a paragraph break after a very short paragraph to buy a vee and fix
an orphaned line on U.S. letter paper.

Also drop an unnecessary paragraph break in glilypond(1).