code: function(value, start, end) {
  			// create modification range
  			var r = range(start, _.isUndefined(end) ? 0 : end - start);
  			var delta = value.length - r.length();
  			
  			var update = function(obj) {
  				_.each(obj, function(v, k) {
  					if (v >= r.end)
  						obj[k] += delta;
  				});
  			};
  			
  			// update affected positions of current container
  			update(this._positions);
  			
  			// update affected positions of children
  			_.each(this.list(), function(item) {
  				update(item._positions);
  			});
  			
  			this.source = require('utils').replaceSubstring(this.source, value, r);
  		}
docs: Replace substring of tag's source
  @param {String} value
  @param {Number} start
  @param {Number} end
  @private