Not Node() but string onlye

Hello,

I am using this:
<xsl:when test="not(node()) and string(.)">

To test if a node has "No Child Nodes" but contains "String only".
So example:

<!-- This should FAIL above test -->
<mynode>
    I hope
</mynode>

<!-- This should FAIL above test -->
<mynode>
    <wishing>
        I wish
    </wishing>
</mynode>

Thanks for your suggestions!
Karl