Pitch, duration, ties, and lyrics are all represented within the MusicXML note element. For example, the E-flat that starts bar 3 in the voice part has the following MIDI-compatible elements:
<note> <pitch> <step>E</step> <alter>-1</alter> <octave>5</octave> </pitch> <duration>24</duration> <tie type="start"/> <lyric> <syllabic>end</syllabic> <text>meil</text> <extend/> </lyric> </note>
In MIDI, a pitch is represented by a single number. MusicXML divides pitch up into three parts: the step element (A, B, C, D, E, F, or G), an optional alter element (-1 for flat, 1 for sharp), and an octave element (4 for the octave starting with middle C).
The pitch represents the sound, not what is notated, so an alter element must be included even if represents a flat or sharp that is part of the key signature. This is why the E-flat contains an alter element, though there is no accidental on the note.
Alter values of -2 and 2 can be used for double-flat and double-sharp. Decimal values can be used for microtones (e.g., 0.5 for a quarter-tone sharp), but not all programs may convert this into MIDI pitch-bend data.
For rests, a rest element is used instead of the pitch element. The whole rest in 3/4 that begins the voice part is represented as:
<note> <rest measure="yes"/> <duration>72</duration> </note>