spec css3 text line break around replaced elements

Line Break Opportunities around Replaced Elements

Background

1. The 2013 LC defines replaced elements are U+FFFC.
2. LC issue #4 points out that it's not web-compatible.
3. The current ED fixed by forcing a soft wrap opportunity both before and after replaced elements.
4. This fix broke Emoji, Gaiji, and all other inline graphics within text scenario where the LC supported nicely.

Proposals

1. Keep the current fix. Web-compat, but inline graphics within text breaks poorly.
2. Revert the fix. Breaks the web, but better design and is better compliant with UAX#14.
3. Keep the current fix for web-compat, add a property to opt-in to the new behavior (e.g., line-break-as: ideographic).
4. Keep the current fix for web-compat, add a property to opt-in to the new behavior in Level 4.

Notes

1. www-style thread
2. Summary by fantasai (member ML)