2.1.421 Part 1 Section 220.127.116.11, summaryLength (Percentage of Document to Use When Generating Summary)
a. The standard does not explicitly state that the summaryLength element can be removed when a document is saved.
Word does not round trip this setting unless certain operations related to automatic summaries are performed while the document is open.
b. The standard states that the values of the val attribute are defined by the XML Schema integer datatype.
Word restricts the value of this attribute to be at least 0 and at most 100.