If template contains:
<nowiki><!-- this is a comment --></nowiki>
then the whole thing gets rendered as visible text on the host page.
If template contains:
<!-- this is a comment -->
then none of it gets transcluded.
Really just want to put some invisible text on the host page-- doesn't have to be an HTML-comment.
This doesn't get transcluded either:
<span style="display:none">Hidden Span</span>