I'm not sure this is something more general in the MathML module or if it's specific to the vertical bar in this particular context, but here is a minimal example showing that the "=0" at the end of the equation is disappearing: \usemodule[mathml] \starttext \xmlprocessdata{}{<imath> <math xmlns='http://www.w3.org/1998/Math/MathML'> <mi>A</mi> <mfenced open="(" close=")" separators=""> <mi>B</mi> <mo>|</mo> <mi>C</mi> </mfenced> <mo>=</mo> <mn>0</mn> </math> </imath>}{} \stoptext And here is a workaround using <mtext> instead of <mo> for the vertical bar which makes the "=0" magically reappear again: \usemodule[mathml] \starttext \xmlprocessdata{}{<imath> <math xmlns='http://www.w3.org/1998/Math/MathML'> <mi>A</mi> <mfenced open="(" close=")" separators=""> <mi>B</mi> <mtext>|</mtext> <mi>C</mi> </mfenced> <mo>=</mo> <mn>0</mn> </math> </imath>}{} \stoptext Flagged up mainly in case it is a bigger problem than just vertical bars in this specific context. Thanks, Duncan