Rather than declaring help context IDs directly, UI controls use help keys (that is, helpKey constants). Though meaningless to the Eclipse help system, helpKey constants provide an abstraction in the Java code from the actual help context IDs and help search expressions.
Each helpKey constant is used to reference an actual help context ID string and a corresponding help search expression, which are defined in properties files (one each for help context IDs and help search expressions).
Any plug-in can contribute the helpKey properties files for a UI component by declaring an extension to org.eclipse.datatools.help.helpKeyProperties in its plugin.xml file. For example, a dedicated context-sensitive help plug-in could contribute both the helpKey properties files and the Eclipse context XML files, independent of the UI plug-in and the UA content contributor (online documentation) plug-in.
Similar to externalized messages, helpKey constants are declared as public static final String in an interface class.
UI components must implement a helpKey constants interface class to reference the externalized help context IDs in a ResourceBundle properties file.