Created attachment 304391 [details] Testcase STR 1. load the attached testcase and look at the output in the console ACTUAL RESULTS "contents" "inline" EXPECTED RESULTS "" "block" Safari does not support display:contents (the rendered red border proves that) so 'contents' should be rejected as a valid value for the 'display' property.
<rdar://problem/31082273>
This looks fixed in Safari 14 & STP.