code: function(className) {
  		if (this.classList) {
  			this.classList.add(className);
  		}
  		else if (!has.call(this, className)) {
  			this.className += " " + className;
  		}
  	}
docs: @function can-util/dom/class-name/class-name.add className.add
  @parent can-util/dom/class-name/class-name
  @signature `className.add.call(el, cls)`
  
  Add a class name to a DOM node if it is not already there.
  
  ```js
  var className = require("can-util/dom/class-name/class-name");
  
  className.add.call(el, "container");
  ```
  
  @param {String} className A string representing a single class name token
  
  @return {void}