css-tree/lib/syntax/function/expression.js

A tool set for CSS: fast detailed parser (CSS → AST), walker (AST traversal), generator (AST → CSS) and lexer (validation and matching) based on specs and browser implementations

// legacy IE function
// expression( <any-value> )
export default function() {
    return this.createSingleNodeList(
        this.Raw(null, false)
    );
}