Controls can be defined on the fly without a library definition or running generation steps. These controls are also called notepad controls.
When several controls should be developed for reuse in different applications, we recommend to create a control library instead of using these notepad controls. Control libraries have additional features like automatic support for theming and right-to-left languages, but the implementation of the controls is the same as for notepad controls.
This functionality is not restricted to controls, but can also be used to create or extend arbitrary objects derived from sap.ui.base.Object.