With my patches for bug 276358 and bug 276317, I'm able to make it render as I expect, similar to what Chrome does. However, the <mtext> in the reference files has a larger height compared to the <mi> in the padding-border-margin-004.html. The RenderMathMLBlock layout seems more complex than the RenderMathMLToken one (for the case when we paint a mathVariantGlyph directly). Maybe RenderMathMLToken should do something special for text-only token elements, see https://w3c.github.io/mathml-core/#layout-of-mtext Alternatively, probably fixing 202302 would do the job too since in that case we won't need special handling for mathVariantGlyph.