+ (object-callbacks . ((Y-common . ,ly:axis-group-interface::calc-y-common)
+ (pure-relevant-grobs . ,ly:axis-group-interface::calc-pure-relevant-grobs)
+ (pure-relevant-items . ,ly:axis-group-interface::calc-pure-relevant-items)
+ (pure-relevant-spanners . ,ly:axis-group-interface::calc-pure-relevant-spanners)
+ (pure-Y-common . ,ly:axis-group-interface::calc-pure-y-common)))