2.1.867 Part 4 Section 3.14.4, ddeLink (DDE Connection)
a. The standard does not specify length limits on @ddeService.
Office enforces a minimum of 1 character and a maximum of 255 characters for @ddeService.
b. The standard does not specify length limits on the ddeTopic attribute.
Office restricts the ddeTopic attribute to 255 characters.
c. The standard does not place a restriction on the maximum length of the ddeService attribute concatenated with the ddeTopic attribute.
Office requires that the combined length of the ddeService and ddeTopic attributes be less than 255.
d. The standard does not place restrictions on the inclusion of '[' or ']' in the ddeService and ddeTopic attributes.
Office requires that the concatenation of the ddeService attribute followed by the ddeTopic attribute contain at most one pair of square brackets ('[' and ']'), and that the opening bracket precede the closing bracket.