2.1.1863 Part 4 Section, FmlaMacro (Reference to Custom Function)

a.   The standard indicates that the FmlaMacro element applies to an object but does not explicitly define a set of valid objects.

Excel supports FmlaMacro on objects defined by all values of the ST_ObjectType simple type except LineA, Note and RectA.

b.   The standard states that the values of this element are defined by the XML Schema string datatype.

Office defines the values of this element with the ST_Macro (§3.9.2, ST_Macro) simple type.