update and extend docs related to options item builder

Author: gearsdigital

public/index.html

@@ -254,15 +254,37 @@ <h2>Options</h2>
 
     /*
      * Type: String or Function
-     * Description: Define how each option should be rendered inside its <li> element.
+     * Description: Define how each option should be rendered inside its &lt;li&gt; element.
      *
      *              If it's a string, all keys wrapped in brackets will be replaced by
      *              the respective values in itemData. Available keys are:
-     *              'value', 'text', 'slug', 'disabled'.
+     *              'value', 'text', 'slug', 'index'.
      *
-     *              If it's a function, it will be called with the following parameters:
-     *              (itemData, element, index). The function must return a string,
-     *              no keys will be replaced in this method.
+     *              If it's a function, it will be called with the following parameter:
+     *              (itemData). The function must return a string. If available all keys
+     *              will be replaced by the respective values in itemData.
+     *
+     *              itemData&lt;Object&gt; {
+     *                 className // Type: String.          Description: option class names.
+     *                 disabled  // Type: Boolean.         Description: option is disabled true/false
+     *                 selected  // Type: Boolean.         Description: option is selected true/false
+     *                 element   // Type: HTMLDomElement.  Description: current select element
+     *                 index     // Type: Number.          Description: current option index
+     *                 slug      // Type: String.          Description: option slug
+     *                 text      // Type: String.          Description: option text
+     *                 value     // Type: String.          Description: option value
+     *              }
+     *
+     *              EXAMPLE:
+     *
+     *              function(itemData) {
+     *                  return '<span class="item-{index}">{text}</span>';
+     *              }
+     *
+     *              // you're free to build and return your own strings
+     *              function(itemData) {
+     *                  return itemData.text + '(' + itemData.index + ')';
+     *              }
      */
     optionsItemBuilder: '{text}',