I've been messing around with applying different CSS styles to blocks and found out quickly that you can't really style the titles of a block much because the titles don't hold much text. When designing a block, I have to split it into two parts, a poorly styled title, and a content area that can be very highly customized. I'm also stuck with a fixed gap between the two.
It seemed to me that if I could have the ability to optionally NOT display the title, then I could have more control over the look of my block using CSS. I tried not entering a title, but that was forbidden. I decided that I should create a code and place it at the front of my title. If the theme engine spotted the code, it would not emit the title. I decided that the code had to be reasonably unique, and settled on !!invisible!!
I managed to achieve my goal by replacing the line (in xtemplate.engine):
$xtemplate->template->assign($key == "subject" ? "title" : $key, $value); // TODO: standardize on 'title' (ie. rename all $block["subject"] to "title")
with:
$xtemplate->template->assign($key == "subject" ? "title" : $key, (substr($value, 0, 13) == "!!invisible!!" ? "" : $value)); // TODO: standardize on 'title' (ie. rename all $block["subject"] to "title")
Once that's done, any titles that start with !!invisible!! will not be displayed. That let me make blocks which were one text line in height, and others which had elaborately styled titling. Maybe someone else might be interested in this hack.