code: function cssToAST(text, syntax, filename) {
    var string = JSON.stringify;
    var fileInfo = filename ? ' at ' + filename : '';
    var tree;
  
    try {
      tree = gonzales.parse(text, {syntax: syntax});
    } catch (e) {
      throw new Error('Parsing error' + fileInfo + ': ' + e.message);
    }
  
    // TODO: When can tree be undefined? <tg>
    if (typeof tree === 'undefined') {
      let message = `Undefined tree ${fileInfo}: ${string(text)} =>
                    ${string(tree)}`;
      throw new Error(format(message));
    }
  
    return tree;
  }
docs: Converts CSS string to AST.
  
  @param {String} text CSS string
  @param {String} [syntax] Syntax name (e.g., `scss`)
  @param {String} [filename]
  @returns {Array} AST