The ZoomSelectedLayers widget zooms to the extents of a selected layer.  The
code looks for the layer metadata "SELECTED" to be "1".  Here's an example
widget def:

                              <!-- ZOOMSELECTEDLAYERS -->
                              <td><cwc2 type="ZoomSelectedLayers" visible="true"
imagetip="Zoom to selected layers" image="icons/icon_zoomactive.png"
styleresource="NavButtons" imagewidth="24" imageheight="24">
                                      <image state="normal"/>
                                      <image state="hover"/>
                                      <image state="selected"/>
                              </cwc2></td>

Also:

- the layer MUST be queryable
- there is a BUFFER parameter that can be set.  Valid values are 0 - 100, 1 is
the default.  It is a percent value.
- do NOT include this in the Toolset...unless u want an enless loop of fun