code: @Nullable
    public static Element getFirstChildElementOfName (@Nullable final Node aStartNode,
                                                      @Nonnull @Nonempty final String sTagName)
    {
      if (aStartNode == null)
        return null;
      return new ChildElementIterator (aStartNode).findFirst (filterElementWithTagName (sTagName));
    }
docs: Search all child nodes of the given for the first element that has the
  specified tag name.
  
  @param aStartNode
  The parent element to be searched. May be <code>null</code>.
  @param sTagName
  The tag name to search.
  @return <code>null</code> if the parent element has no such child element.