All components inherit properties from their ancestor classes. When you derive a new component from an existing one, your new component inherits all the properties of its immediate ancestor. If you derive from one of the abstract classes, many of the inherited properties are either protected or public, but not published. 

To make a protected or public property available at design time in the Object Inspector, you must redeclare the property as published. Redeclaring means adding a declaration for the inherited property to the declaration of the descendant class.