WebKit implements the following non-standard APIs: - Document#onsearch - Element#onsearch - the `search` event Neither Firefox nor Edge implement these. Blink *does* implement these APIs, but the Blink maintainers are currently investigating the impact of its removal [1]. That issue includes references to the `incremental` attribute, but I have not seen any indication of its existence in WebKit. WebKit currently has at least one open bug concerning the behavior of this feature [2]. [1] https://github.com/whatwg/html/issues/667 [2] https://bugs.webkit.org/show_bug.cgi?id=13786
<rdar://problem/48937114>
Tests added in https://github.com/web-platform-tests/wpt/pull/19889 The test results suggest WebKit does support an incremental attribute.