Jmac/demo merge

[jmacarthur]

This is a collection of features added before and after the internal demo. Some bits could do with more documentation (especially highlighting, which uses magic numbers) but this should be enough to start working on the svg merging work.

[palvarez89]

I'll merge as is, and fix up the "error" later, if needed (it's just only a log output)

[jmacarthur]

Thanks palvarez89, and yes it was meant to be 'target' in the second clause.