The CSSWG recently decided that block margins should NOT be cloned on each fragment, so we should remove that from our implementation (but only for blocks). https://lists.w3.org/Archives/Public/www-style/2015May/0279.html - RESOLVED: box-decoration-break clones margins (note this only affects inlines) ... box-decoration-break & margins ------------------------------ fantasai: Last is about box-decoration-break and margins, and whether "clone" clones margins. fantasai: If I have a box with a border, and it breaks, there's two ways to handle it. fantasai: First is to just slice the box, so no border at slice. fantasai: Other is to wrap the border around fully for each piece. fantasai: So question is whether to clone margins too. fantasai: So if you had margin-top, does that show up at the top of the next fragment? Florian: Margin-collapsing? fantasai: Interesting. [Florian was pointing out that margins at unforced fragmentation breaks collapse to nothing.] dbaron: And what if multiple collapsing elements have differing values for box-decoration-break? [This doesn't seem to be an actual problem, each box does what it does.] fantasai: Current behavior is to restart the next page at the border box; no cloning of margins. Rossen: Yeah, anything else can get weird, especially with negative margins. box-decoration-break & margins (cont.) -------------------------------------- fantasai: And I think issue 13 is that it doesn't matter; margins get collapsed into the pagination break. Rossen: Yeah. dbaron: Margins don't disappear for inlines, right? fantasai: Right. dbaron: Presumably box-decoration-break applies to inlines, too. fantasai: Yes. fantasai: So yeah, inlines are still a problem. No strong opinion, but since inline margins don't normally collapse into the line edge, I think we should keep it (clone inline margins) RESOLVED: box-decoration-break clones margins (note this only affects inlines) [Snack break] <dbaron> FWIW, Gecko's implementation of box-decoration-break:clone on inlines does agree with what we just resolved <dbaron> i.e., we do clone the margins

It was implemented in bug 1025669 (part 1).

Pushed by aethanyc@gmail.com: https://hg.mozilla.org/integration/autoland/rev/e9783a644016 Stop cloning block direction margins for box-decoration-break:clone. r=mats