Barlines
Barlines are indicated by a token starting with an equals sign. A optional number can immediately follow the equals sign, representing a measure number. VHV will display the bar number at each system break, excluding a label for measure 1:
Following the measure number can be an optional styling for the barline. - means an
invisible barline, || is a double thin barline, |!: is a left-repeat,
:|!|: is a left-right repeat. A special style is ==, representing a final
barline. This bar usually does not include a bar number, since it is the last
one in the piece/movement.
Humdrum can represent more barline styles, but the above types are currently supported in verovio.
Pick-up measures
Typically the initial barline should be labeled in the Humdrum
encoding even though it is not printed. Either =1 or =1- should
be used at the start of the first measure (with - meaning an
invisible barline), but the starting barline will be automatically
suppressed if it is a regular barline. Labeling the first bar is
necessary if you need to extract it by measure number with a tool
such as myank.
Pickup beats do not have a barline at their start. If a measure
does not match the duration of the time signature at the start of
the music and the data does not start with a barline, it will be
automatically interpreted as a pick-up measure and automatically
assigned 0 as the measure number for use with the myank filter.
Here is example music with a pick-up beat, and a typical ending that drops the duration of the pickup measure: