code: function addPhaseTrigger(priv, target, propertyName) {
    check(target, 'target').is.anEventTarget();
    var property = propertyName || 'transform';
    check(property, 'property').is.aString();
  
    if (property === 'transform') {
      property = feature.transformPropertyName;
    }
    priv.phaseTriggers.put(property, target);
    maybeStart(priv);
  }
docs: Adds passed target to phase triggers.
  
  Phase will be automatically set to next each time a `transitionend` event of matching
  **target** and **propertyName** bubbles up to Phaser's container element.
  
  @param {Node} target (typically DOM Element) that will trigger next phase when matched
  @param {String} propertyName will trigger next phase when matched (optional, defaults to 'transform')
  @precondition **target** has container element as ancestor (see ${link Phaser.prototype.constructor})
  @precondition given pair of **target** and **propertyName** is not already a phase trigger
  
  @fqn Phaser.prototype.addPhaseTrigger