Hi Bob,
Actually I think I just answered my own question... And it seems to have been a pretty daft one at that, as I was already doing something very similar!
I try to not ask pointless questions, sorry.
I will give an explanation, anyway.
I'm using my own snippets wherever possible to aggregate content.
I am pulling docs from containers and aggregating them in places like a sidebar, etc.
I find that my clients are not very good at formatting content, so I do things like make preformatted image fields for them. I am trying to make my snippets slightly more general purpose, and was wanting to have:
load chunk with opening block;
if(image is blank) load chunk without formatted image block;
else(image is present) load chunk WITH image block, and put image in it;
if(introtext is not blank) load chunk with intro text and read-more button;
else load chunk with content;
load chunk with closing block;
This is (sortof) the kind of thing one would do to render a webpage in a MVC style framework.
It looks like I can load several chunks, though; I am looping through resources, arrayifying them and loading them into chunks, and it works. So I think I just have to follow that principal - build the output, then output the output.
(please excuse my terminology, I'm [obviously] self-taught.)