Some technical documents are related to each other. There are main manuals and documents that report changes, additional information and corrections related to a main manual in a specific edition. Those documents are called Addenda. Thus, a main manual can have one or more Addendas.
If you look in the document list from a main manual point of view at this relationship, you will notice that if addenda exist, a link "Related Documents" is being displayed. Clicking on this link lists all related addenda.
Looking at this relationship from an addenda point of view, you will also see the Link "Related Documents". Clicking on it, lists the main manual and all other related addenda.