function onComment( block, text, start, end ) {
		if ( block ) {
			// TODO: add support for highlighting multi-line comments.
			return;
		}
		tokens.push({
			'type': 'comment',
			'start': start,
			'end': end
		});
	}
Callback invoked upon encountering a `Comment` when parsing.

@private
@param {boolean} block - boolean indicating whether a comment is a block comment
@param {string} text - comment value
@param {number} start - start index
@param {number} end - end index