code: function(done) {
      var isSync = (typeof done !== 'function');
      var sass = require('node-sass');
      var opts = this.sassTemplateOptions();
      var self = this;
  
      if (isSync) {
        try {
          var result = sass.renderSync(opts);
          return this.fieldIdentifiersToInterpolations(result.css.toString());
        } catch (err) {
          throw formatSassError(err, opts.data);
        }
      }
  
      sass.render(opts, function(err, result) {
        if (err) return done(formatSassError(err, opts.data));
        done(null, self.fieldIdentifiersToInterpolations(result.css.toString()));
      });
    }
docs: Low-level implementation of template rendering.
  @param {Function} callback for asynchronous rendering.
  @returns {String|undefined} rendered template string (sync) or undefined (async).
  @private