An external module in the Archiving and Interchange DTD Suite that is first set up in the Module to Name the Modules (%modules.ent;) and is then called from the MathML setup module (%mathmlsetup.ent;) to include the MathML elements in the tag set for the DTD.
<!ENTITY % mathml.dtd PUBLIC "-//W3C//DTD MathML 2.0//EN" "mathml2.dtd" >
modules.ent