On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 48 on 2016-01-20
In Chrome Android version 48 on 2016-01-26
In Edge version 79 on 2020-01-15
In Firefox version 50 on 2016-11-15 Note: Before Firefox 50, the plaintext value was ignored for vertical writing modes (bug 1302734). Before Firefox 15, plaintext didn't do anything to an inline element. The specification changed and the implementation was changed in Firefox 15.
In Firefox for Android version 50 on 2016-11-15 Note: Before Firefox for Android 50, the plaintext value was ignored for vertical writing modes (bug 1302734). Before Firefox for Android 15, plaintext didn't do anything to an inline element. The specification changed and the implementation was changed in Firefox for Android 15.
Not in Internet Explorer
In Quest Browser version 5.0 on undefined
In Opera version 35 on 2016-02-02
In Opera Android version 35 on 2016-02-04
In Safari version 11 on 2017-09-19
In Safari on iOS version 11 on 2017-09-19
In Samsung Internet version 5.0 on 2016-12-15
In WebView Android version 48 on 2016-01-26
In WebView on iOS version 11 on 2017-09-19