An annotation used to specify some swing-related information for the automatically generated
BeanInfo classes. This annotation is not used if the annotated class has a corresponding user-defined
BeanInfo class, which does not imply the automatic analysis.
The isContainerfeature attribute was introduced primarily for the Swing library. All Swing components extend the Container class by design, so the builder tool assumes that all Swing components are containers. The BeanInfo classes with the isContainer attribute allow to directly specify whether a Swing component is a container or not.