Testing for following text()

How can I test if there is a text node following and restrict the test
to a certain parent element?
In the example I'd like to test if there is text following after the
<s/> element up to the enclosing end tag of the <b> element.
This test should fire at the first s element because of the following
BBB text, but not at the second s element in spite of the following AAA
text.
The structure below the b element may contain any number of nesting
levels and element.
I'd like to include the test in a template which tackles the s element,
like <xsl:template match="s[some-test]">

--- Example -------------------------
<a>
  aaa
  <b>
      bbb
      <c>
          ccc
          </s>
      </c>
      BBB
  </b>
  AAA
  <b>
      bbb
      <c>
          ccc
          <s/>
      </c>
  </b>
   AAA
</a>
--- /Example -------------------------