quail doesn't stop me from typing English into Chinese mode

[Dan Jacobson]

Often I forget to toggle-input-method and start typing English when
the computer is still expecting Chinese, ending up with ㄕoㄨ ㄌaㄅeㄌ
instead of "show label" which is what I thought I typed before I
looked up at the screen.

In other leading brands of input software, I would be already
triggering all kinds of warning bells, and my cursor would already
have been stopped by the highway patrol.  Is there a option to "don't
allow nonsensical input" for quail?   Or a function "convert mistaken
input back to English", "toggle-input-method-retroactively"?
-- 
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