src/main/java/com/bazaarvoice/jless/parser/Parser.java
@MemoMismatches
    Rule MixinReference() {
        Var<String> name = new Var<String>();
        return FirstOf(
                // No arguments, reference an existing rule set's properties
                Sequence(
                        SelectorGroup(), ';',
                        resolveMixinReference(NodeTreeUtils.getFirstChild((InternalNode) pop(), SelectorNode.class).toString(), null),
                        Ws0Nodes()
                ),
                // Call a mixin, passing along some arguments
                Sequence(
                        Class(), name.set(match()), Arguments(), Ws0(), ';',
                        resolveMixinReference(name.get(), (ArgumentsNode) pop()),
                        Ws0Nodes()
                )
        );
    }
@MemoMismatches
    Rule MixinReference() {
        Var<String> name = new Var<String>();
        return FirstOf(
                // No arguments, reference an existing rule set's properties
                Sequence(
                        SelectorGroup(), ';',
                        resolveMixinReference(NodeTreeUtils.getFirstChild((InternalNode) pop(), SelectorNode.class).toString(), null),
                        Ws0Nodes()
                ),
                // Call a mixin, passing along some arguments
                Sequence(
                        Class(), name.set(match()), Arguments(), Ws0(), ';',
                        resolveMixinReference(name.get(), (ArgumentsNode) pop()),
                        Ws0Nodes()
                )
        );
    }
SelectorGroup ';' Ws0
/ Class Arguments ';' Ws0