Selection is based in DOM tree, so if have the following HTML structure:
<div id="source" style="-webkit-flow-into: content;">inside region inside region inside region</div>
<div id="outside-region">outside region outside region outside region</div>
<div id="region" style="-webkit-flow-from: content;"></div>
If you select text from "outside region" to "inside region" the highlighted area is exactly the opposite to what the user is actually selecting.
This might seem weird from the user point of view, but it is ok following the DOM tree according to editing specs (https://dvcs.w3.org/hg/editing/raw-file/tip/editing.html).
This was not working since r139197 (because of it didn't allow to select content from different flow threads) and it got fixed in r155058. So, we should add a Layout Test to avoid break it again in the future without noticing.
Created attachment 211920 [details]
Comment on attachment 211920 [details]
Clearing flags on attachment: 211920
Committed r155974: <http://trac.webkit.org/changeset/155974>
All reviewed patches have been landed. Closing bug.