This is not part of SVG 2.0 but of the discontinued module SVG Animations 2. Please do not look at this spec.

Created attachment 478712 [details] testcase https://w3c.github.io/svgwg/specs/animations/#:~:text=the%20attributeType%20attribute%20is%20not%20supported%20by%20SVG > Unlike SMIL Animation, the attributeType attribute is not supported by SVG. SVG's animation elements follow the behavior defined for the auto value of attributeType. That is, when determining if ‘attributeName’ corresponds to an attribute name or a CSS property name, the implementation must first search through the list of CSS properties for a matching property name. If no matching property is found, the implementation must search for a matching attribute on the target element. https://wpt.live/svg/animations/attributeTypes.html Through https://github.com/w3c/svgwg/commit/968d1a83a5c29f6107e01df3b44b172a17cedc90 https://www.w3.org/2015/02/12-svg-minutes.html#:~:text=can%20we%20discuss%20attributeType=%22auto%22 Gecko https://bugzilla.mozilla.org/show_bug.cgi?id=1062106 The test is not really testing attributeType. https://github.com/web-platform-tests/wpt/blob/eec31fe936/svg/animations/attributeTypes.html I'm adding the same testcase without attributeType and it is still passing on all browsers.