I'm writing some typography software which allows users to specify lengths in various dimensions.
If the user asks for a length of "1ex", is it reasonable to determine this length from the sxHeight entry in the OS/2 table? Should I be literally measuring the point height of an "x" in the font instance? Or something else?
Similarly for "1em" - I'm just using the point size of the font instance but should I be doing something more clever?
And "1en" - half an em?