p:choose

p:choose selects one branch based on an XPath expression.

<p:choose>
  <p:declare-input .../>
  <p:declare-output .../>

  <p:when test="...">
    {components}
  </p:when>

  ...

  <p:otherwise>
    {components}
  </p:otherwise>
</p:choose>

The declare-input associates an input a local port name. This input is
used as the context for the XPath expression in each when statement.
Each of the when's (and the otherwise) must assign outputs to the
declared outputs.

The output(s) of the selected branch will appear on the declared
output port(s) when the choose finishes.

It is an error if the choose has declared outputs and no p:when
matches and no p:otherwise is provided.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
XML Standards Architect
Sun Microsystems, Inc.