When you want to view a document Online, for example Word Document, the Url of the document is :
The GUID is the UniqueID of the document in SharePoint.
It would be very interesting to select an older version of the document to view using a syntax like underneath (for the revision 1 of a document) as when you want to download a specific revision of a document?
For Downloading the revision 1 of MyDocument.docx the syntax is :
For viewing this underneath URL could be great: