Usually, we don't need the more powerful features of jPDL when defining pageflows. We do need the <decision> node, however:

<decision name="evaluateGuess" expression="#{numberGuess.correctGuess}">
    <transition name="true" to="win"/>
    <transition name="false" to="evaluateRemainingGuesses"/>
</decision>

A decision is made by evaluating a JSF EL expression in the Seam contexts.