2.1.792 Part 1 Section 18.104.22.168, worksheetSource (Worksheet PivotCache Source)
a. The standard allows both ref and name attributes.
Office requires one and only one of these attributes.
b. The standard states that the id attribute contains a relationship to a sheet part.
Office uses the id attribute to specify a relationship to an external workbook.
c. The standard limits @name to any length string.
In Office, @name has a limit of 255 characters, and cannot be empty.
d. The standard limits @sheet to any length string.
In Office, @sheet has a limit of 31 characters.