This article covers a Hippo CMS version 7.7. There's an updated version available that covers our most recent release.

Configure the linkpicker to select folders or filter on document type 

How to make the link picker of the mirror field select folders or certain other document types

In console, go to your template under:
/hippo:namespaces/[your_namespace]/[your_doctype]/ editor:templates/default/[your_mirror_field]/cluster.options.

On this node with primary type frontend:pluginconfig, you can have a multi-value property named nodetypes. If you put here hippostd:folder you should be able to pick folders. If you also want to be able to pick documents, also add hippo:document.

On the same node as stated above, you can set a property named base.uuid which can contain the UUID of the starting location of the picker dialog.

Similar configuration for the link picker of the Xinha HTML field

The Xinha editor has also a link picker (the CreateLink Xinha plugin) that can be configured to select types.

Enabling picking certain types from the CreateLink Xinha plugin

In console, go to the node /hippo:namespaces/hippostd/html/editor:templates/default/root/Xinha.plugins.CreateLink 
In the multi-valued string property named nodetypes you can define the types, for instance set the values hippostd:folder and hippo:document

The above changes behaviour on the Xinha plugin level, so it is available all document types that use it.

Enabling picking certain types from document type

For a more fine grained configuration on the document type level, go to /hippo:namespaces/[your_namespace]/[your_doctype]/editor:templates/default/[your_path_name]/cluster.options

On that node, use a multi-valued string property named linkpicker.nodetypes with the desired values.