App-specific Browser Layers

The design prototype defines a number of site sections, or “Apps”, that contain content. The same content types are styled differently per app. We can have News Items in the workspaces app, in the news app, but also in the library app.

This means that, unlike stock Plone, we need different view registrations for content types, depending on the context: a News Item default view in workspaces that is different from the News Item default view in library.

Browser Layer Switching

Registering different default views, depending on the app context, is done by registering these default views to app-specific browser layers.

By default, all such app-specific browser layers are disabled. Within an app context, only the browser layers specific for that app are switched on.

This ensures that multiple default view registrations for Plone content types do not conflict, because they are registered for different app-specific browser layers of which only the “right” one is active within the intended app context.


If you look at WorkspaceContainer:

class WorkspaceContainer(AbstractAppContainer, Container):
    A folder to contain WorkspaceFolders.
    Implements IAppContainer to enable workspace-specific content view

    app_name = "workspace"  # should not contain dots
    app_layers = (IWorkspaceAppContentLayer, IWorkspaceAppFormLayer)

You can see it defines it’s app name “workspace” and switches on two app layers. The actual switching is done by the AbstractAppContainer mixin, see below.

Those two app layers will only ever be active within a workspace. This makes it easy to then register an override the default Document view that is specific for the workspace design in ploneintranet/workspace/basecontent/configure.zcml:


Within the library app, a different default Document view is registered in ploneintranet/library/browser/baseviews.zcml:


These two registrations use different custom view classes and different templates to provide different default views for Document, depending on whether the Document lives in a Workspace or within the Library.


ploneintranet.layout defines an app protocol where traverse hooks on the site root and on app containers disable/enable specific browser layers.

On traversal of the INavigationRoot, all IAppLayer layers are removed from the request. This traverse hook is globally registered.


On traversal of an IAppContainer, only the IAppLayer layers as defined in the app_layers attribute of that IAppContainer are activated. This traverse hook needs to be registered separately for every IAppContainer implementer.

This is typically done by using the mixin class AbstractAppContainer which registers a beforeTraverse hook on the app object.

The actual layer manipulation is done in ploneintranet/layout/

Note that the implementation here necessarily has a bit of overlap with Theme Switcher.

Adding a custom app layer

To register a browser layer that is only active within a specific app container:

  • subclass your layer from ploneintranet.layout.interfaces.IAppLayer
  • mark your app container as providing ploneintranet.layout.interfaces.IAppContainer
  • implement IAppContainer on your app container, which requires:
    • set app_name = ‘myname’
    • set app_layers = (yourcustomlayer,)
    • call register_app_hook() on __init__() (not needed if you inherit from AbstractAppContainer as first mixin)

See for an easy mixin. See ploneintranet.layout.tests.utils.MockFolder for an example implementation.

from import Folder
from import AbstractAppContainer
from ploneintranet.layout.interfaces import IAppContainer
from ploneintranet.layout.tests.utils import IMockLayer
from zope.interface import implements

class IMockFolder(IAppContainer):
    """Marker interface for an app container"""

class MockFolder(AbstractAppContainer, Folder):
    """A mock folder that inherits the app registration hook
    from AbstractAppContainer."""

    app_name = 'mock'
    app_layers = (IMockLayer, )

Obviously you should use your actual browser layer for the app instead of IMockLayer.

For content types that are available in multiple apps, you can now register app-specific views by binding those views to your custom app layer. See ploneintranet.workspace.basecontent for a number of views on generic content types, registered specifically for workspace-contained content only.

Body class marking for app content and views

Some parts of the site render conceptually within the Apps section. Some IAppContainer objects, like workspaces and the library, conceptually render outside the Apps section.

Note that both workspaces and the library are not proper apps in terms of the prototype, but we still need to mark them in order to be able to switch Diazo rules on and off.

content: in-app app-foo

Content containers that implement IAppContainer result in the marking of the respective app as a css class on the body of the view response.

ploneintranet.layout.browser.policy detects the traversal of an IAppContainer and sets “in-app app-foo”. This can be used to switch Diazo transforms on.

Currently this is used do apply different Diazo templates to “app-workspace” content, than to “app-library” content.

view: view-app app-bar

Some apps do not have a special context at all, but consist only of views that render on the INavigationRoot.

However, in the UI we want to be able to style such views differently and be able to set e.g. CSS classes on the body element, to indicate that we’re looking at an app, and at which app.

To mark your view as an App view, make sure it implements ploneintranet.layout.interfaces.IAppView. This involves marking the interface on your view, and providing the app_name attribute.


from ploneintranet.layout.interfaces import IAppView
from zope.interface import implements

class BarApp(BrowserView):
    """A view that is part of an app but renders on the siteroot"""
    app_name = 'bar'

ploneintranet.layout.browser.policy detects that an IAppView is active and sets body classes “view-app app-bar”. This can be used to switch Diazo templating.

The logo viewlet override checks for both the IAppContainer (on the context) and IAppView (on the view) to determine how it handles breadcrumbs handling.