code: function(block, pos, ctx, callback) {
    if (block.hasOwnProperty('htmlslabs')) {
      outputSlabs(block.htmlslabs, ctx, callback);
    } else {
      if (formats.hasOwnProperty(block.format)) {
        formats[block.format](block, pos, ctx, callback);
      } else {
        callback(new Error('unknown format: ' + block.format));
      }
    }
  }
docs: Output a text block in HTML.
  
  Warning: This assumes that you have used validateTextBlock or makeTextBlock
  to ensure a valid XSS-free textblock.
  
  @param {Object} block The text block to be output
  @param {String} pos The position to start adding suffixes to (useful for generating links or pagination)
  @param {Object} ctx An object to be passed to all of the rendering functions
  @param {Function} callback A callback called with (err, text)