vars ?keep_vars ?warn stylesheet substitutes var(--name) references with the value of the corresponding --name declaration and deletes the definition, but only for a variable with a single definition (its value is then unambiguous). A variable in keep_vars, or one redefined in a different scope (a real cascade override such as dark mode), keeps its definition and stays a live var() reference. warn is called with each name (leading --) that could not be inlined because it is redefined in a different scope.

decode_import_url s strips the url(...) wrapper and any surrounding quotes from an @import URL string as held in Stylesheet.import_rule.url. The parser preserves the verbatim source form there for round-tripping; this helper recovers the bare URL.

imports ?query ?layer_order loader stylesheet replaces every @import rule in stylesheet with the body of the imported stylesheet looked up through loader. Imports the loader cannot resolve are left in place; a cyclic @import is broken by dropping the second visit. The walk descends into nested at-rules and rule bodies, so imports declared inside them are inlined too; the caller is responsible for preloading loader.imports with every transitively-referenced stylesheet body.