Ah! Now understand the problem.
That will work if you use >_ for quoting. That will give 2 spaces in total, and only one will be trimmed.
Also in Blockquotes - could spec require strict indent before/after ">"? i suggested to make trimming equal for all inner strings. That could reduce problem for multiline blockquotes, when user don’t use space after >
But i agree, my solution is not ideal too. Stats from real docs needed to decide. I don’t use HTML at all, and will be fine if your suggestion accepted instead of mine. I like it and have no breaking examples.