Becky has the right of it.
Red squiggly lines for misspelled (according to primary & secondary spell-check dictionaries) in Code View.
The Spellcheck Editor dialog will spellcheck words in multiple languages as determined by the lang and xml:lang attributes on html tags.
That's how it was left in the discussion/feedback thread from earlier in the fall, anyway:
https://www.mobileread.com/forums/sh...d.php?t=331060.