2.1.1580 Part 1 Section 126.96.36.199, cxnSp (Connection Shape)
a. The standard states that cxnSp connects two sp elements.
In Office, cxnSp connects two sp or pic elements.
b. The standard states that the values of the macro attribute are defined by the XML Schema string datatype.
Office requires that the macro attribute value follow the same grammar as name-references ("[ISO/IEC-29500-1] §188.8.131.52") with a minimum length of 0 characters and a maximum length of 256 characters.