Get child text from an xml element in a mapping

Content

Implementing the suggestion in this topic - Include mapped output as the value of another output..., I need to get the text content of an XML node returned from a REST Adapter invoke so I can encode it to Base64.  I tried just passing the node to the encodeBase64 function, but it encoded the text representation of the node itself (i.e. element name, attributes, etc...) rather than the text content of the node.  It seems that the way to do this is with a for-each and then get-content-as-string, but I am unable to add a for-each  as the input to the encode function.  I thought to assign the value to a variable, but I can't