Description

Authors can specify an image to be used in place of the border-style. In this case, the border’s design is taken from the sides and corners of an image specified

Rationale

• "buginess" is one of the often cited reasons for lack of use.

• will likely never be high priority without a concerted effort to fix.

• mostly bugs around border-image-repeat round and space values

• big bug in chrome which makes using border-image at all difficult
  https://bugs.chromium.org/p/chromium/issues/detail?id=767352

• might need tests for vector vs raster border-image-source??
  https://bugzilla.mozilla.org/show_bug.cgi?id=1778032
  https://bugs.chromium.org/p/chromium/issues/detail?id=1342292

Specification

https://drafts.csswg.org/css-backgrounds/#border-images

Tests

https://wpt.fyi/results/css/css-backgrounds?label=experimental&label=master&aligned
note that there are some border-image tests are titled css3-border-image for some reason.