+ (barNumberFormatter ,procedure? "A procedure that takes a bar
+number, measure position, and alternative number and returns a markup
+of the bar number to print.")
+ (barNumberVisibility ,procedure? "A procedure that takes a bar
+number and a measure position and returns whether the corresponding
+bar number should be printed. Note that the actual print-out of
+bar numbers is controlled with the @code{break-visibility} property.
+
+The following procedures are predefined:
+
+@table @code
+@item all-bar-numbers-visible
+Enable bar numbers for all bars, including the first one and broken
+bars (which get bar numbers in parentheses).
+
+@item first-bar-number-invisible
+Enable bar numbers for all bars (including broken bars) except the
+first one. If the first bar is broken, it doesn't get a bar number
+either.
+
+@item first-bar-number-invisible-save-broken-bars
+Enable bar numbers for all bars (including broken bars) except the
+first one. A broken first bar gets a bar number.
+
+@item first-bar-number-invisible-and-no-parenthesized-bar-numbers
+Enable bar numbers for all bars except the first bar and broken bars.
+This is the default.
+
+@item (every-nth-bar-number-visible @var{n})
+Assuming @var{n} is value@tie{}2, for example, this enables bar numbers
+for bars 2, 4, 6, etc.
+
+@item (modulo-bar-number-visible @var{n} @var{m})
+If bar numbers 1, 4, 7, etc., should be enabled, @var{n}@tie{}(the modulo)
+must be set to@tie{}3 and @var{m}@tie{}(the division remainder) to@tie{}1.
+@end table")
+