!2 The Sub Page widget.
Sometimes we want to conveniently create a link to a sub page.  We could do this by using the syntax ''!-SuperPage.SubPage-!'', but this is inconvenient.  Instead we want to be able to say ''!-^SubPage-!''.

!|Page creator.|
|Page name.|Page contents.|Page attributes.|valid?|
|SuperPage|^SubPage||true|

!|Response Requester.|
|uri|valid?|contents?|
|SuperPage|true||

The widget should translate into a ? link of the form:
 * ''!-^SubPage-!<a title="create page" href="!-SuperPage.SubPage-!?edit&nonExistent=true">[?]</a>''
!|Response Examiner.|
|type  |pattern|matches?|value|
|contents|\^SubPage<a title="create page" href="SuperPage.SubPage\?edit&nonExistent=true">\[\?\]</a>|true||

If the sub page is already present, then the widget should translate into a normal link.

!|Page creator.|
|Page name.|Page contents.|Page attributes.|valid?|
|SuperPage.SubPage|nothing||true|

!|Response Requester.|
|uri|valid?|contents?|
|SuperPage|true||

!|Response Examiner.|
|type  |pattern|matches?|value|
|contents|<a href="SuperPage.SubPage">\^SubPage</a>|true||
