It seems like '-compact' needs to come before the columns from mdoc(7)? For whatever reason, the pattern in siginfo.3 and sigevent.3 is also to omit the final column.

siginfo(3)/sigevent(3) use Sy (bold) rather than Em (italic) for column headings FWIW.

+1, this might further improve navigating around the manual page.

The manual list -type first (-column is the type) and -compact last in the synopsis. It gives no admonition that it must be first. A quick google search doesn't turn it up either. And none of the man pages in the source tree do that either. I don't see that either siginfo.3 or sigevent.3 use -compact... I'll keep it last...

But I can get 2 more characters from Description if I remove trailing white space in System and Subsystem headings. I can get away w/o having the final column arg, so I'll do that.

Sure. Easy enough.

Yes. Added a comment to the commit message.

I was referring to this part of the mdoc(7) manual:

Bl -type [-width val] [-offset val] [-compact] [col ...]
     Begin a list.  Lists consist of items specified using the It macro,
     containing a head or a body or both.

Clearly, the optional list of columns [col ...] comes after the optional -compact. I was worried that If the parser was like getopt(3) it would assuming all tokens after the first one that doesn't start with - are column widths, thus treating -compact as a column width. However, it seems like the parser doesn't work like that since it does seem to render the same both ways.