What determines the set of fonts that can be set in Equation Tools in MS Word 2007 and newer?

Question

In Microsoft Word 2007 and newer, if you enter Equation Tools and then click on the Equation Options buttons (the very small button in the lower right corner of the Tools group in the Design tab), the first setting in the window that opens is “Default font for math regions”. I suppose it normally contains Cambria Math only. It sets the overall font used, the font used for everything but such “Normal Text” (i.e., text formatted as “Normal Text” with the Equation tools—for such text, normal font setting commands of Word are available).

The question is: How can the repertoire of fonts there be expanded? In my computer, the menu (dropdown) has Cambria Math, XITS Math, Asana Math, and STIX Math. Does this mean that Word constructs the menu by looking at the names of installed fonts and picks up those that have names ending with the word “Math”? Is this documented somewhere?

For example, if I wanted to use FreeSerif in equations, would I thus need to create a version of it with a name (internal name) that ends with “Math”?

This is the settings window that the question is about:

Answer 1

I'd guess that Word looks for fonts that have the appropriate OpenType Math tables. Unlike the old equation editor, which could use any font and the result would be horrible regardless, Word requires the font to be properly set up for math, which includes lots of fun things, like e.g. kerning at corners of symbols, not usually required for text.