KERML — Some bindings have optional connector end multiplicities

Clauses 8.4.4.6.2 (Binding Connectors) and 7.4.6.3 (Binding Connector Declaration) says they have end multiplicity 1..1 on both ends:

Binding connectors are binary connectors that require their source and target features to have the same values on each instance of their domain. They are typed by the library association SelfLink (which only links things in the modeled universe to themselves, see 9.2.3.1) and have end multiplicities of exactly 1. This requires a SelfLink to exist between each value of the source feature and exactly one value of the target feature, and vice-versa.

The connector ends of a binding connector always have multiplicity 1..1.

but there is no constraint for this on BindingConnector, which might be good because the libraries sometimes have optional mutiplicities, for example:

Occurrences:
  binding unionsOf.union[0..1] = self[1];
Transfers:
  private binding instant[0..1] of startShot[0..1] = endShot[0..1]
Control Performances:
  binding loopBack of untilDecision.elseClause[0..1] = whileDecision[1];

might be others.

SelfLink connectors with one optional end multiplicity are equivalent to feature subsetting (without the inheritance restrictions), rather than the typical meaning of "bind". Perhaps these should have a different textual keyword?