## Here is an example for groff.

syntax groff "(/tmac\.[^/]+$|\.(m[ems]|rof|tmac)$)"
comment ".\""

# The argument of .ds or .nr
color cyan "^\.(ds|nr) [^[:space:]]*"
# Single-character escapes
color brightmagenta "\\."
# The argument of \f or \s in the same color
color brightmagenta "\\f." "\\f\(.." "\\s(\+|\-)?[0-9]"
# Newlines
color cyan "(\\|\\\\)n(.|\(..)"
color cyan start="(\\|\\\\)n\[" end="]"
# Requests
color brightgreen "^\.[[:space:]]*[^[:space:]]*"
# Comments
color yellow "^\.\\".*$"
# Strings
color green "(\\|\\\\)\*(.|\(..)"
color green start="(\\|\\\\)\*\[" end="]"
# Characters
color brightred "\\\(.."
color brightred start="\\\[" end="]"
# Macro arguments
color brightcyan "\\\\\$[1-9]"