So, what happens is that in Opera, for zero-length ranges (ie, just a caret, no selection):

• .getSelection().getRangeAt(0) returns a Range
• but then .getClientRects() returns an empty ClientRectList
• and .getBoundingClientRect() returns a rectangle with all values being 0

This seems to work:

range = document.getSelection().getRangeAt(0)

Range

span = document.createElement('span')

<span/>

range.getClientRects()

ClientRectList []

range.surroundContents(span)

undefined

$(span).offset()

{ left: 352, top: 1025 }

Now we just have to substract window.scrollY from the 'top' value and remove the <span> from the DOM again. (And don't call .getClientRects() on that Range again, as it returns a completely bonkers huge list of values.)

Related URL: https://gerrit.wikimedia.org/r/61190 (Gerrit Change I4bad882d1d6fb83bcdcfd0de3bfc9af52960c2ff)

Hmm, apparently this also happens for non-empty selections in some cases. We're gonna need a larger workaround...

(Done is PS2.)

The fix is merged now. Marking as fixed.