Occasionally, an application may want a component of its user interface to be
visible but temporarily unavailable for input. For example, a menu might be used
to present all application commands, although some commands may
not be valid at all times.
Therefore, a contact can either be ``sensitive'' or ``insensitive'' to input.
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When a contact is insensitive, events of the following type are not dispatched
to the contact and are ignored.
<UL>
<LI><#2279#><TT>:button-press</TT><#2279#>
</LI>
<LI><#2280#><TT>:button-release</TT><#2280#>
</LI>
<LI><#2281#><TT>:enter-notify</TT><#2281#>
</LI>
<LI><#2282#><TT>:focus-in</TT><#2282#>
</LI>
<LI><#2283#><TT>:focus-out</TT><#2283#>
</LI>
<LI><#2284#><TT>:key-press</TT><#2284#>
</LI>
<LI><#2285#><TT>:key-release</TT><#2285#>
</LI>
<LI><#2286#><TT>:leave-notify</TT><#2286#>
</LI>
<LI><#2287#><TT>:motion-notify</TT><#2287#>
</LI>
</UL>
Also, the sensitivity of a contact is typically represented visually. For
example, an insensitive contact may be displayed in a distinctive color, greyed
out, or stippled.
<P>
A contact is insensitive if the value of its <#2289#><TT>sensitive</TT><#2289#> slot is <#2290#><TT>:off</TT><#2290#>, or if its parent is insensitive. Conversely, a contact is sensitive if and
only if it and all of its ancestors have a value of <#2291#><TT>:on</TT><#2291#> for <#2292#><TT>sensitive</TT><#2292#>.
