Have the related docs plugin only suggest similar documents through search that are of the current site's content

The suggestions should not suggest documents from another language, or another version in the case of the Hippo campus.

Thus, in the case below

content
documents
site1
site2

site1 its documents should not contain suggestions from site 2: Otherwise, you might get suggestions from other languages and in case for Hippo campus of other versions

Since the CMS does not have the concept of 'root site content node' we'll take as root content node the following:

When we want to get similar documents for some document, we'll traverse from the root node to the document that we are now editing and take the first node which has mixin hippotranslation:translated. If we do not find such a node, we'll do the search from the jcr:root

Thus, if we edit document

/content/documents/mysite-en/news/2012/mydoc

then we check for content, then /content/documents, etc, until we have found a node with the mixin. I choose not to traverse up, as I am not sure a hippo:handle has the mixin for example.