Since you have defined attribute “displayMode” as type Boolean, so it can be assigned with true of false.
Then your comment is opaque. What does “’has value” mean? True or false?
Further study: http://help.sap.com/saphelp_uiaddon10/helpdata/en/56/2803c6f55c49608d01a453cc0590ab/frameset.htm if we are in ui component context, we do not need to concatenate id prefix and id body manually, as suggested by sap help above: Create all views, controls, and elements in a UI component by using the this.createId() method and retrieve them by using the this.byId() method.