On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 1 on 2008-12-11 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Chrome Android version 18 on 2012-06-27 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Edge version 12 on 2015-07-29
In Firefox version 1 on 2004-11-09 Note: The behavior of element.getElementsByTagNameNS changed between Firefox 3.5 and Firefox 3.6. In Firefox 3.5 and before, this function would automatically case-fold any queries so that a search for "foo" would match "Foo" or "foo". In Firefox 3.6 and later this function is now case-sensitive so that a query for "foo" will only match "foo" and not "Foo". For more background on this, please see the comment from Henri Sivonen about the change. You can also look at the relevant part of the standard, which states which parts of the API are case-sensitive and which parts aren't. Before Firefox 19, this method was returning a NodeList; it was then changed to reflects the spec change.
In Firefox for Android version 4 on 2011-03-29 Note: Before Firefox 19, this method was returning a NodeList; it was then changed to reflects the spec change.
In Internet Explorer version 9 on 2011-03-14
In Quest Browser version 5.0 on undefined Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Opera version ≤12.1 on undefined Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Opera Android version ≤12.1 on undefined Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Safari version 1 on 2003-06-23 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Safari on iOS version 1 on 2007-06-29 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In Samsung Internet version 1.0 on 2013-04-27 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In WebView Android version 4.4 on 2013-12-09 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.
In WebView on iOS version 1 on 2007-06-29 Note: Initially, this method was returning a NodeList; it was then changed to reflect the spec change.