Browsers ignoring Bidi Embedding Controls is probably not web-compatible

[SimonSapin]

https://w3c.github.io/unicode-xml/#Bidi

3.3 Bidi Embedding Controls (LRE, RLE, LRO, RLO, PDF), U+202A..U+202E

[…]

What to do if detected: In a browser context, ignore.

This is apparently not what browsers do. data:text/html,&%23x202e;Test renders at tseT in both Firefox and Chromium. Assuming this is interoperable with other browsers too, there is probably a lot of existing content that relies on this code points affecting the bidi algorithm. Changing browsers to ignore these code points would break that content.

[r12a]

I think this is the same as / related to #7

[duerst]

This is definitely related to #7, but not the same:

#7 is about what should (in the view of the commenter) happen.

This issue is about what happens in actual browsers.

[SimonSapin]

Unfortunately, except for brand new features, what I find useful in specifications as a browser implementer has much to do with what needs to happen for compatibility with legacy content (even if it seems absurd, see quirks mode) and little to do with what should ideally happen if the Web was new and didn’t have this legacy.

Maybe this document containing "guidelines" and being a Note (not on the REC track) means it’s not a specification? But the "What to do if detected" phrasing make it look like one.