Layout widget

[nexushoratio]

Stealing ideas from w2ui.

Five panels:

+--------------+
|     TOP      |
+---+------+---+
| L | MAIN | R |
|   |      |   |
+---+------+---+
|    BOTTOM    |
+--------------+

<div id=container>
  <div id=top>
  </div>
  <div>
    <div id=left>...</div>
    <div id=main>...</div>
    <div id=right>...</div>
  </div>
 <div id=bottom>
 </div>
</div>

• Widget enhancements #190
• widget adapters for common types #191
• ARIA roles of concern
  • Window splitter
    • Splitters are associated with a Primary pane, which in our case here, would probably be TOP/BOTTOM/LEFT/RIGHT
    • Support arrow keys when have focus
    • Draggable
    • Role is separator
    • aria-orientation (horizontal, vertical)
    • aria-valuenow is (roughly) %age open (resizable only)
    • Needs one of aria-label, aria-labelledby (resizable-only)
    • Needs aria-controls that points to primary pane element (that is, what it controls)
• Generate divs appropriately (all always present, even if empty or disabled)
• Each panel accessible via name property
• Simplify code by always initializing panels in the constructor
• Support destroy()
• Export
• Address this: If a variable holding a widget is set to a new value, the previous widget should be explicitly destroyed.
• Each exterior pane needs a way to specify the min/max/natural size and whether resizable or not (some of this can be done with installStyle(), but not all)