Specifications MML provides for different modules that are used for different purposes. There are modules addressing the physics of music from a structural point of view.
Some modules address the 'add-ons' to the basic structure.
There are MIDI-related modules and also a Universal Synthesizer module. And there is of course a Western notation module. MML elements and attributes are listed separately, but are also briefly discussed in their relevant modules. You can thus either begin reading the modules , or consult a reference section for elements and attributes .