In the documentation of every object attribute you will find information about the applicability of this attribute. Attribute applicability is described in the form of a combination of the four letters I, S, G, and N. This tells you the various contexts that the attribute can be used in.
Here is an explanation of the different applicability contexts:
For example, if an attribute has an applicability of just "I", then this attribute can only be used during object initialization time. It cannot be changed later using mui.Set(). If an attribute has an applicability of just "S" on the other hand, it is not possible to specify the attribute already at initialization time in the XML file. Attributes that have an applicability of "ISGN" can be used in all contexts.