2.1.706 Part 4 Section 3.4.12, t (Text)

a.   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.

b.   The standard places no restrictions on the length of the value of the t element.

Excel restricts the value of this element to 32767 characters.