- NB. This doesn't mean an Item has to initialize the output field before
- spacing calculation.
-
-
- Element properties
-
- visibility-lambda -- a function that takes the break
- direction and returns a (transparent, empty) cons
-
- breakable -- boolean indicating if this is a breakable item (clef,
- barline, key sig, etc.)
-
- */
-class Item : public Score_element