#createMarkup creates markup for dates and numbers in the given text,
#e.g. 'On Oct. 21, the Dow Jones rose to 10043 points' should become
#'<mytxt>On <date>Oct. 21</date>, the Dow Jones rose to <number>10043</number> points</mytxt>
sub createMarkup {
   my ($text, $doc) = @_;
   #create parent node
   my $node = new XML::DOM::Element ($doc, 'mytxt');
   #markup dates
   my $textNode = $node->addText ($text);
   markupElement ($textNode, $node, \&findDate, 'date');
   
   #markup numbers
   foreach my $child ($node->getChildNodes ()) {
      next unless $child->isTextNode ();
      my $frag = $child->getNodeValue ();
      markupElement ($child, $node, \&findNumber, 'number');
   }
   return $node;
}

sub markupElement {
   my ($textNode, $parent, $rFindFunc, $elemName) = @_;
   my $doc = $parent->getOwnerDocument ();
   die unless $textNode->isTextNode ();
   my $nextNode = $textNode->getNextSibling ();
   my $text = $textNode->getValue ();
   while (my ($before, $elem, $after) = &$rFindFunc ($text)) {
      $textNode->setValue ($before);
      my $elemNode = new XML::DOM::Element ($doc, $elemName);
      $elemNode->setValue ($elem);
      $parent->insertBefore ($elemNode, $nextNode);
      $textNode = $doc->createTextNode ($after);
      $parent->insertBefore ($textNode, $nextNode);
      $text = $after;
   }
}