Huh, I'd never heard of decomposed/precomposed before and I kind of skimmed over them in the original article. Looking at your example, I still can't figure out what the difference is between the two (I guess the Playground editor itself just can't represent the difference?). I'll have to go read up on that concept.

Edit: Having read about them, I guess I assumed that if my keyboard inputs an ë it's actually inputting those two underlying characters. Or to put it differently, I assumed there weren't two separate representations for the same character; that the "decomposed" and "precomposed" versions are one in the same, at the byte level. Learned something h̶o̶r̶r̶i̶f̶y̶i̶n̶g̶ new!