This attribute has an NMTOKENS value, meaning a space-separated list of values, so that a document can declare that it may include both TeX and images, for example, or MathML, gif images, and TeX. If the document includes no math, this optional attribute may not be present. Likely values include:

mathml   tex   latex   images   plain-text 

Listing the types of math presentation a document may use is not quite the same as describing all the math representations a system must have to show the math in the document, as some of the math representations may be inside <alternatives> elements. In that case, a user/rendering application is expected to choose the most appropriate of the alternatives to display.