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A boolean value, "false" by default, which indicates whether this component reference
can have its targets overridden by a composite reference which promotes the
component reference.
If @nonOverridable==false, the target(s) of the promoting composite reference
replace all the targets explicitly declared on the component reference for any
value of @multiplicity on the component reference.
If the component reference has @nonOverridable==false and @multiplicity 1..1
and the reference has a target, then any composite reference which promotes
the component reference has @multiplicity 0..1.by default and MAY have an explicit @multiplicity of either
0..1 or 1..1.
If @nonOverridable==true, and the component reference has @multiplicity 0..1 or
1..1 and the component reference also declares a target, promotion implies
that the promoting composite reference has @wiredbyImpl==true and the composite
reference cannot supply a target, but can influence the policy attached to the
component reference.
If @nonOverridable==true, and the component reference @multiplicity is 0..n
or 1..n, promotion targeting is additive