I have a wiki where some tiddlers are automatically displayed with a dedicated template. This template adds some chrome around the content of the tiddler on display. That content can be wikitext, that needs to de interpreted on block mode.
I found out that in order to do that, the template has to code
The reason that <$transclude $field=text mode=block/> doesn’t work as expected is that the presence of a parameter starting with $ triggers modern mode, which means that the mode parameter also needs to be passed as $mode.
The action of {{!!text}} depends on the context. On its own, with a blank line before and after, it will generate a block mode transclusion. Embedded in text, it will generate an inline mode transclusion.