code: function (o, cb) {
      if (!o.out) {
        throw new Error('output dir missing');
      }
  
      this.src(o)
        .on('error', handleCallbackError(cb))
        .pipe(vfs.dest(function (file) {
          return file.base;
        }))
        .on('error', handleCallbackError(cb))
        .on('end', function () {
          if (_.isFunction(cb) && !error) {
            cb();
          }
        });
    }
docs: /*
  creates sprite and style file and save them to disk