What if we extend the mkgmap style language with an 'import' or 'include' directive familiar from other languages? There already is the base-style directive (used in resources/styles/marine/info), but it allows a style to import only one other style.
There is no real reason why it should be restricted to one. Attached patch fixes that. If you have a style "c" which has base-style: a base-style: b Then style c will pull in the rules from a and b, so that rules in c will come first, followed by those in b and then those in a. They are in reverse order because the rule that matches is first is the one that gets picked and we want c to override b and b to override a. Both a and b can have their own base-style options and so on, as now. ..Steve