DocBook contains elements that serve as "wrappers" for mathematics but does not, itself, provide for formatting and display of mathematical expressions. To actually create mathematical formulae, the tool set has support for ASCIIMath.

To activate this support, your document must have at least one element, anywhere in the document, that has a role attribute of "`text(am)text(ath)`". I usually put this on the DocBook wrapper elements for mathematics such as informalequation or inlineequation.

A typical sequence for creating a line of mathematics, then, is to insert an informalequation just after a paragraph. xxe will automatically insert a mathphrase inside the informalequation. Within the mathphrase you can type text. Type the reverse apostrophe (the one under the ~ key on most keyboards), then one or more spaces, then the equation you want (in the ASCIImath format), then one or more spaces, then close with another reverse apostrophe.