I'm wondering if we've got something like this...

http://www.macs.hw.ac.uk/~alison/ds98/node114.html

So I imagine that if I use the function described here to test each side of a box, it'll work against a line...

I know, it looks daft, me answering my own question, but if anyone's got a function ready rolled for this job, I'd still like to see it.