The staves element indicates the number of staves in a musical part, which in this case is 2 staves for the piano part. The staves element is optional. If it is not present, as is the case in the voice part, there is 1 staff for the part.
The clef element is used to indicate the clef for the staff. By specifying the clef’s sign and its line, MusicXML handles both the common treble and bass clefs along with tenor, alto, percussion, tab, and older clefs. The treble clef definition indicates that the second line from the bottom of the staff is a G; the bass clef definition indicates that the fourth line from the bottom of the staff is an F. The number attribute indicates the staff number if the part has more than one staff.
The clef element may also contain a clef-octave-change element after the line element. This is used for clefs that are written either an octave higher or lower than sounding pitch. For example, the tenor line in choral music is usually written in treble clef, an octave higher than the notes actually sound.
The clef for this part would be represented as:
<clef> <sign>G</sign> <line>2</line> <clef-octave-change>-1</clef-octave-change> </clef>
While attributes usually appear at the start of a measure, they can appear anywhere within the measure. Mid-measure clef changes are the main use for this feature.
To represent common and cut time signatures, use the symbol attribute of the time element.
For common time, use:
<time symbol="common"> <beats>4</beats> <beat-type>4</beat-type> </time>
For cut time, use:
<time symbol="cut"> <beats>2</beats> <beat-type>2</beat-type> </time>
Without the symbol attribute, these time signatures would appear as 4/4 and 2/2, respectively.