TActionLink descendants call IsCaptionLinked to determine whether they need to propagate changes to the Caption property of the action so that they are reflected by the client object. When IsCaptionLinked returns true, the action controls the Caption property: Changes to the Caption property of the action are reflected by changes to the corresponding property of the client object. When IsCaptionLinked returns false, the client object does not reflect the Caption property of its action, either because it does not have a corresponding property, or, more commonly, because it manages the value of its corresponding property independently. 

As implemented in TActionLink, IsCaptionLinked merely checks that the Action property specifies a descendant of TCustomAction (that is, it is an action that has a Caption property). Descendant classes override IsCaptionLinked to determine whether the Caption property is linked with the appropriate client property. 

Caption 

Caption 

SetCaption 

Action