Properties related to spacing around text should be proportional to text size

If your lyrics are 8pt, you could just about get away with a space between words of 0.2sp:

But if your lyrics are 12pt you certainly can't:

But since this value doesn't scale, you have to remember to change the size and the spacing setting together.

Similarly, frame padding of 0.2sp is maybe fine for 8pt text:

But not really for 30pt text:

Which is the same problem. There are other settings like this (including many of the lyrics ones, and dash width/gaps/thickness for all sorts of text) which would benefit from the same treatment.

We should have at the very least the option for these and similar settings to be proportional to the text size, which is perhaps most easily achieved by expressing them in ems rather than sp.