I would like to copy something to the target XML doc context (!) depending from the value of a node on the same level.

It should all look similar to the following pseudo code:

...assume we are on level/inside <aaa><bbb><ccc>
<xs:if <ddd>...</ddd> contains a non-whitespace value then>
  <mytext>yes value found<mytext>
<xs:else>
  <myothertext>no value found</myothertext>
</xs:if>
...
</ccc>...</bbb>....</aaa>

How can I code this with XSLT ?

Again: If possible the condition should be context dependent. I don't want to code
the full XPath  /aaa/bbb/ccc/ddd in the "if" clause.
Instead the XPath expression should be relative to the current position

Thank you 
Ben