Bug 126414 [Commands] handlers: Provide help context ids
For commands and handlers to replace actions, they need to be capable of providing help context identifiers. For an example, see OpenResourceHandler in org.eclipse.ui.ide. This help context id will need to be definable through XML and through code.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
throw new NotDefinedException(
					"Cannot get the return type of an undefined command"); 
		}
		return returnType;
	}
	/**
	 * Returns whether this command has a handler, and whether this handler is
	 * also handled and enabled.
	 * 
	 * @return <code>true</code> if the command is handled; <code>false</code>
	 *         otherwise.
	 */
	public final boolean isEnabled() {
		if (handler == null) {
			return false;
		}
		return handler.isHandled() && handler.isEnabled();
	}
	/**
	 * Returns whether this command has a handler, and whether this handler is
	 * also handled.
	 * 
	 * @return <code>true</code> if the command is handled; <code>false</code>
	 *         otherwise.
	 */
	public final boolean isHandled() {
		if (handler == null)
			return false;
		return handler.isHandled();
	}