This is for when bug 99620 is fixed. I'm not sure I see tests for AccessibilityRenderObject::isMathOperator() (<mo> renderers or the anonymous created by <mfenced>) AccessibilityRenderObject::isMathFenceOperator() (fences created by <mfenced>) AccessibilityRenderObject::isMathSeparatorOperator() (separators created by <mfenced>) After bugs 99620 is fixed, we will have the following attributes: <mo fence="true"> => isMathFenceOperator <mo separator="true"> => isMathSeparatorOperator <mo separator="true" fence="true"> => isMathFenceOperator && isMathSeparatorOperator (not sure this really exists in real math) Also, the values can be determined from the operator dictionary (http://www.w3.org/TR/MathML3/appendixc.html). For example the two markup should be equivalent for the AT: <math><mo>(</mo><mi>x</mi><mo>,<mo><mi>y</mi><mo>;</mo><mo>]</mo></math> and with explicit attributes <math><mo fence="true">(</mo><mi>x</mi><mo separator="true">,<mo><mi>y</mi><mo separator="true">;</mo><mo fence="true">]</mo></math> Similarly, we should have the equivalence between mfenced and its expanded form. See http://www.w3.org/TR/MathML3/chapter3.html#presm.mfenced