Looks like some *roff/mandoc markup snuck into the tmux man-page:
$ man tmux | grep -2 "Ar target"
-l requests the clipboard from the client using the xterm(1)
escape sequence. If Ar target-pane is given, the clipboard is
sent (in encoded form), otherwise it is stored in a new paste
buffer.
Based on my super-weak *roff/mandoc markup knowledge, that looks
like it's supposed to be a macro to mark `target-pane` as an argument
with .Ar and I don't know if it needs the parallel of an HTML/XML
closing tag to mark the end.
Figured I'd mention it since doc issues are normally treated as
bugs.
-tkc
