Here’s a little gotcha I just ran into again recently. I’ve got a new folderish Plone content type that I’m working on, to which I’d like to be able to add plain-old Pages. At first, my profiles/default/types/NewFolderish.xml looked like this:

...
<property name="filter_content_types">True</property>
<property name="allowed_content_types">
  <element value="Link" />
  <element value="Page" /> <!-- WRONG -->
</property>
...

Well, that didn’t allow me to add a page to a New Folderish content type.  Here’s why: for GenericSetup, you have to identify a content type by it’s meta_type. For most default content types, it’s what you’d expect. For Page and Collection, it’s not. Here’s the correct profiles/default/types/NewFolderish.xml

...
<property name="filter_content_types">True</property>
<property name="allowed_content_types">
  <element value="Link" />
  <element value="Document" /> <!-- CORRECT -->
</property>
...

To allow a Page

  <element value="Document" />

To allow a Collection

  <element value="Topic" />

Happy Ploning!