This is more restrictive than the original grammar because it requires at least one attribute. I don't know if that matches the implementation. But it would be easy to fix by allowing color_spec to expand to either a bare face-name or to face-name + ':' + attributes.
diffr --help
prints this:This means that a
color_spec
always ends with a colon, but I'm sure this wasn't intended. Maybe reword like this:This is more restrictive than the original grammar because it requires at least one attribute. I don't know if that matches the implementation. But it would be easy to fix by allowing
color_spec
to expand to either a bareface-name
or toface-name + ':' + attributes
.