2.1.670 Part 1 Section 18.3.2.10, 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.