The main point of this article is that the standard version of Content MathML can be extended and customized by modifying the XSLT stylesheet that translates the Content MathML into Presentation MathML. Documents with the modified Content MathML will display with no furhter work in the Firefox browser, because this browser supports XSL transformations. For browsers that support Presentation MathML only, the author can process the document with an XSLT processor (such as the one built into Firefox) and then publish the output document, with Presentation MathML. Finally, the author can convert the document to PDF with a standard Print-to-PDF application. Thus, a modified and extended version of Content MathML can be viewed as an authoring platform for Presentation MathML.
My hope is that readers of this article can see how they might customize Content MathML to suit their own authoring habits and areas of mathematical interest.