Check if next tag is ...

The XML file I work with contains records that most of the time have
three unique nodes. However, it is part of the design that one of these
nodes, T in the example, is optional. Here is an example of a file.

<A>
<C>
  <P>AAA</P>
  <T>BBB</T>
  <S>CCC</S>
</C>
<C>
  <P>DDD</P>
  <T>EEE</T>
  <S>FFF</S>
</C>
<C>
  <P>GGG</P>
  <S>HHH</S>
</C>
</A>

           P            T            S
C        AAA       BBB       CCC
C        DDD       EEE       FFF
C        GGG         *          HHH
C          ....          ...            ....

The problem I'm having is that I'm trying to test when processing the P
node if the next node is T. If the next node isn't T or if the T node
doesn't exist then use the value * instead. Now I've experiemented with
following-sibling, node() and value but haven't been successful.

Can anyone point me in the direction of a good tutorial or help me out.
My current list of references during development are:
[1] - http://www.zvon.org/xxl/XSLTreference/Output/index.html,
[2] - http://www.dpawson.co.uk/xsl/sect2/sect21.html=20
But these haven't been able to help me do what I want to do.