my can be used as a short form of
compositeFor(this) when using with colon-operators used (only) with composites. For example, the pair of examples below have the same functional effect:
Thus the use of 'my' makes for more compact code; it has no effect on performance.
If using compositeFor() in an any other context, e.g. a composite of which the current note is not a member then the 'my' designator can not be used.