docs: function (fp, cb) {
      if (typeof fp === 'function') {
        cb = fp;
        fp = null;
      }
  
      if (typeof cb !== 'function') {
        throw new Error('async `write` was called without a callback function.');
      }
  
      var dest = fp || this.dest.path;
      var src = this.src.path;
      var str = this.content;
  
      if (str) {
        lazy.write(dest, str, cb);
      } else {
        lazy.copy(src, dest, cb);
      }
  
      this.emit('write', dest);
      return this;
    }