Ambitus indicate pitch ranges for voices.
Accidentals only show up if they are not part of the key signature. AmbitusNoteHead grobs also have ledger lines.
Adding the Ambitus_engraver to the Staff context creates a single ambitus per staff, even in the case of staves with multiple voices.
As demonstrated in the second measure, such analysis brackets can be nested.
Accidentals are available in different ancient styles, which all
are collected here.