It was designed explicitly to be written by other programs, to the point that they have an "error message" element for when your latex-like parse-and-output-mat

It was designed explicitly to be written by other programs, to the point that they have an "error message" element for when your latex-like parse-and-output-mathml program failed, whose example in the spec is "Syntax error: \frac{1}": https://www.w3.org/TR/mathml-core/#error-message-merror https://www.w3.org/TR/mathml-core/#error-message-merror