defined in <a href="https://github.com/angular/angular/tree/master/modules/angular2/src/core/annotations/di.js#L12">angular2/src/core/annotations/di.js (line 12)</a>
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Specifies that a function for setting host properties should be injected.
NOTE: This is changing pre 1.0.
The directive can inject a property setter that would allow setting this property on the host element.