This is a temporary attribute, similar to 'webkitattachmentpath', used to correctly serialize attachment elements. As such, there's no need for it to persist on the attachment. This could lead to strange behavior, for instance, when performing a continuity copy/paste.
<rdar://problem/36099093>
Created attachment 329632 [details] Dependent on https://bugs.webkit.org/show_bug.cgi?id=180892
Created attachment 329733 [details] Rebase on master
Comment on attachment 329733 [details] Rebase on master Clearing flags on attachment: 329733 Committed r226097: <https://trac.webkit.org/changeset/226097>
This change broke the Windows build: https://build.webkit.org/builders/Apple%20Win%20Release%20%28Build%29/builds/6682