code: function(name, value, pos) {
  			var list = this.list();
  			var start = this.nameRange().end;
  			var editTree = require('editTree');
  			var styles = _.pick(this.options, 'styleBefore', 'styleSeparator', 'styleQuote');
  			
  			if (_.isUndefined(pos))
  				pos = list.length;
  			
  			
  			/** @type XMLEditAttribute */
  			var donor = list[pos];
  			if (donor) {
  				start = donor.fullRange().start;
  			} else if (donor = list[pos - 1]) {
  				start = donor.range().end;
  			}
  			
  			if (donor) {
  				styles = _.pick(donor, 'styleBefore', 'styleSeparator', 'styleQuote');
  			}
  			
  			value = styles.styleQuote + value + styles.styleQuote;
  			
  			var attribute = new XMLEditElement(this, 
  					editTree.createToken(start + styles.styleBefore.length, name),
  					editTree.createToken(start + styles.styleBefore.length + name.length 
  							+ styles.styleSeparator.length, value)
  					);
  			
  			_.extend(attribute, styles);
  			
  			// write new attribute into the source
  			this._updateSource(attribute.styleBefore + attribute.toString(), start);
  			
  			// insert new attribute
  			this._children.splice(pos, 0, attribute);
  			return attribute;
  		}
docs: Adds new attribute
  @param {String} name Property name
  @param {String} value Property value
  @param {Number} pos Position at which to insert new property. By
  default the property is inserted at the end of rule