From Eclipsepedia

IFile object contribution

We also have to provide object contributions (which in the past were scoped by objectClass).

Here's an example from one of our plugin.xml:

<objectContribution adaptable="true“
     objectClass="org.eclipse.core.resources.IFile“
     nameFilter="*.xml“
     id="org.eclipse.jdt.internal.ui.javadocexport.JavadocWizard">
  <visibility>
     <objectState name="contentTypeId“
           value="org.eclipse.ant.core.antBuildFile" />
  </visibility>
  <action label=“Create Javadoc“
        class="o.e.jdt.i.ui.jt.CreateJavadocActionDelegate“
        enablesFor="1" id="LaunchJavadocWizard"/>
</objectContribution>

enablesFor is now a property of the active handler, not the visible GUI element.

Menus

There will be a reserved popup ID, "org.eclipse.ui.popup.any" that will allow contributions to any popup menu.

<extension point="org.eclipse.core.expressions.definitions">
      <definition id="org.eclipse.ui.example.antFile">
         <iterate ifEmpty="false">
            <adapt type="org.eclipse.core.resources.IFile">
               <test property="org.eclipse.core.resources.name" 
                     value="*.xml"/>
               <test property="org.eclipse.core.resources.contentTypeId"
                     value="org.eclipse.ant.core.antBuildFile"/>
            </adapt>
         </iterate>
      </definition>
   </extension>
   <extension point="org.eclipse.ui.menus">
      <menuContribution locationURI="popup:org.eclipse.ui.popup.any">
         <command commandId="org.eclipse.jdt.ui.launchJavadocWizard"
               id="LaunchJavadocWizard"
               label="Create Javadoc"
               style="push">
            <visibleWhen checkEnabled="false">
               <or>
                  <with variable="activeMenuSelection">
                     <reference definitionId="org.eclipse.ui.example.antFile"/>
                  </with>
                  <with variable="activeMenuEditorInput">
                     <reference definitionId="org.eclipse.ui.example.antFile"/>
                  </with>
               </or>
            </visibleWhen>
         </command>
      </menuContribution>
   </extension>

It's probably that the default variable for core expression evaluations would be selection, so you wouldn't need the <with/> clause like in the second item above.

There would probably also be a short-hand to tie the visibility to an active handler. Maybe <visibleWhen handler="true"/> This is still conjecture.

Menus API

Here is a similar example programmatically.

public static void addFileContribution() {
    final IMenuService menuService = (IMenuService) PlatformUI
            .getWorkbench().getService(IMenuService.class);
    // an expression that walks the selection looking for objectclasses
    final ObjectClassExpression ifileExpression = new ObjectClassExpression(
            "org.eclipse.core.resources.IFile");

    final ImageDescriptor postIcon = AbstractUIPlugin
            .imageDescriptorFromPlugin("org.eclise.ui.tests",
                    "icons/full/elcl16/post_wiki.gif");
    final ImageDescriptor loadIcon = AbstractUIPlugin
            .imageDescriptorFromPlugin("org.eclise.ui.tests",
                    "icons/full/elcl16/load_wiki.gif");
    AbstractContributionFactory factory = new AbstractContributionFactory(
            "popup:org.eclipse.ui.popup.any?after=additions") {
        public void createContributionItems(IMenuService menuService,
                List additions) {
            CommandContributionItem item = new CommandContributionItem(
                    "org.eclipse.ui.examples.wiki.post",
                    "org.eclipse.ui.examples.wiki.post", null, postIcon,
                    null, null, null, "P", null,
                    CommandContributionItem.STYLE_PUSH);
            menuService.registerVisibleWhen(item, ifileExpression);
            additions.add(item);

            item = new CommandContributionItem(
                    "org.eclipse.ui.examples.wiki.load",
                    "org.eclipse.ui.examples.wiki.load", null, loadIcon,
                    null, null, null, "L", null,
                    CommandContributionItem.STYLE_PUSH);
            menuService.registerVisibleWhen(item, ifileExpression);
            additions.add(item);
        }

        public void releaseContributionItems(IMenuService menuService,
                List items) {
        }
    };
    menuService.addContributionFactory(factory);
}

The location of org.eclipse.ui.popup.any specifies any context menu, and the expression ties it to a specific objectClass. Using the new expression syntax you can make your conditions more complex.

You can set your visibleWhen expression on each item as you create it.

In 3.3M6 registerVisibleWhen(*) method might be changing.