2.1.717 Part 4 Section 3.7.1, author (Author)

a.   The standard does not limit the length of the value of the author element.

Excel restricts the value of this element to be at most 65535 characters.

b.   The standard makes no mention of an xml:space attribute.

Excel uses this attribute to specify, using the W3C space preservation rules, how white space should be handled for the element's contents; its allowed values are defined by the XML 1.0 specification.