function childContentWrapper(element) {
    var wrapper = undefined;
    for (var c = element.firstChild; c; c = c.nextSibling) {
      var type = c.nodeType;
      wrapper = (type === 1)  // Element Node
          ? (wrapper ? element : c)
          : (type === 3)  // Text Node
          ? (notWs.test(c.nodeValue) ? element : wrapper)
          : wrapper;
    }
    return wrapper === element ? undefined : wrapper;
  }
Given an element, if it contains only one child element and any text nodes
it contains contain only space characters, return the sole child element.
Otherwise returns undefined.
<p>
This is meant to return the CODE element in {@code <pre><code ...>} when
there is a single child element that contains all the non-space textual
content, but not to return anything where there are multiple child elements
as in {@code <pre><code>...</code><code>...</code></pre>} or when there
is textual content.