From the spec: https://w3c.github.io/mathml-core/#new-display-math-value Currently, WebKit fails these associated WPT tests: https://wpt.fyi/results/css/css-display/display-math-on-non-mathml-elements.html?label=master&label=experimental&aligned&q=mathml I don't believe there's currently a bug for this, and a lot of places in the spec also rely on the computed display property being equal to `block math` or `inline math` -- e.g. here with mtext (https://w3c.github.io/mathml-core/#layout-of-mtext): > If the element does not have its computed display property equal to block math or inline math then it is laid out according to the CSS specification where the corresponding value is described.