Implements rendering strategy for tree like components.
| getItemNode | returns HTML element of the item |
| render | renders the specified item or the whole component |
| onAfterRender | occurs immediately after the component has been rendered |
| onBeforeRender | occurs immediately before the component has been rendered |
| onItemRender | for each item rendering, occurs only for items with custom templates |
| onPartialRender | called when part of tree is repainted |