How to dump a variable in SP XML environment?

Question

XML

Hello.
There is a rather old project (WebTutor).
The documentation describes that the pre-executable code is entered in the SP XML environment and JavaScript syntax. I started to google the SP XML documentation , I didn’t find anything similar by analogy with var_dump / print_r, as for example in PHP.
Template files have sections of code wrapped in <% code... %>
For example:

<%
if ( ! curDoc.attributes.no_disp_childs && ! curDoc.attributes.left_disp_childs ) {
  sub_docs = XQuery( 'for $elem in documents where $elem/parent_document_id = ' + curDocID + ' order by $elem/position return $elem' );
            
  if ( ArrayOptFirstElem( sub_docs ) != undefined ) {
    counter = 0;
    for ( _sub_doc in sub_docs ) {
     ........
%>

How is it possible to solve this issue?