The current version of the spec, found at
adds the 'space' keyword to the border-image-repeat property.
border-image properties were implemented in bug 497995 which should have landed. The spec is now CR. This bug might/might not be dependent on bug 713643.
This implementation will be similar to implementation of the background-repeat property in bug 548372.
Added dependence on bug 548372 because it will implement most of the required functionality so fixing this will be easier after it lands.
*** Bug 911632 has been marked as a duplicate of this bug. ***
Safari 9.3 supported: https://developer.apple.com/library/prerelease/mac/releasenotes/General/WhatsNewInSafari/Articles/Safari_9_1.html
I updated the MDN document.
Is this easy following bug 548372?