New folding key for a not standard language

assuming I’m not using a standard programming language bur a proprietary one, is it possible to fold part the code customising the key?

If for example I have something like:

var test;
var result;
include script
return result;

Is it possible to expand the content of “script” customizing somewhere the key “include”?
Please let me know.

Including code that’s not originally in the document isn’t really what folding does. But yes, you can probably program this, though it’s not available as standard functionality.