The fontoxml-mathml add-on provides support for MathML fragments to be edited by and rendered in Fonto.
MathML can be edited using the mathml-edit or open-mathml-editor operations. This functionality is provided by the WIRIS MathType editor. Please refer to its documentation for a list of supported MathML features.
Please note that the MathType editor currently supports a few non-standard extensions to the MathML schema. These generally take the form of attributes in a WIRIS namespace, defaulting to the wrs prefix. The W3C-recommended MathML schema files support such extensions via xs:anyAttribute. It is possible that other MathML processors or derived schemas do not support these extensions. At the time of writing, MathType does not offer a way to disable these features.