to SSI syntax, you can now use ordinary HTML syntax, as in:

  <dtml.in objectIds>
     <dtml.var sequence-item>
  </dtml.in>

Both the new syntax and the SSI syntax are allowed in the same document.
In fact, if you were really twisted, you could:

  <dtml.in objectIds>
     <dtml.var sequence-item>
  <!--#/in-->

;)