Bug 287139 [CommonNavigator] Add core expression to determine initial activation for NCE
Build ID: 20090619-0625 Steps To Reproduce: Currently, the definition of the Navigator Content Extension via plugin.xml allows to specify the boolean attribute allowByDefault which controls if the contributed content is active by default. It makes sence to change the type of the attribute from boolean to core expression, which will allow to evaluate the default context and show content depending on it. This will ease the control of content and enhance the declarative configuration of CNF and NCEs. More information:
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/INavigatorContentDescriptor.java
*         &lt;navigatorContent/&gt; element.
	 *         
	 * @since 3.5        
	 */
	public String getAppearsBeforeId();
	
	/**
	 * Returns the unique sequence number of this extension.  This is calculated based on
	 * the priority and the appears before and represents the order the extension will appear
	 * relative to the other extensions
	 * 
	 * @return The sequence number of the extension
	 *         
	 * @since 3.5        
	 */
	public int getSequenceNumber();
	
	/**
	 * The enabledByDefault attribute specifies whether an extension should be
	 * activated in the context of a viewer automatically. Users may override
	 * this setting through the "Types of Content" dialog.
	 * 
	 * @return true if the extension is enabled by default.
	 */
	boolean isActiveByDefault();
	/**
	 * Determine if this content extension is enabled for the given element.
	 * 
	 * @param anElement
	 *            The element that should be used for the evaluation.