2.1.698 Part 4 Section 22.214.171.124, top10 (Top 10)
a. The standard does not mention any limits on the value of @val.
In Office, if this element is on a pivottable, the @val must be greater than or equal to 0. Otherwise, it must be between 1 and 500 inclusive.
b. The standard does not specify a default value for the filterVal attribute.
Excel uses a default value of 0 for this attribute.