The <principal-voice> element

Parent element: <direction-type>

The principal-voice type represents principal and secondary voices in a score, either for analysis or for square bracket symbols that appear in a score. The element content is used for analysis and may be any text value. The symbol attribute indicates the type of symbol used. When used for analysis separate from any printed score markings, it should be set to none. Otherwise if the type is stop it should be set to plain.