Hi Bob,
If the attributes are tied to the CAD Document, WTPart, or WTDocument, then they must be checked out in order to update the attributes. If the attributes are associated with CAD Document Master, WTPart Master or WTDocument Master then they do not need to be checked out. However, when you update a master attribute you change the value for all iterations of that Master.
For example, you have an attribute defined on WTPartMaster called "color", and you have the following:
Part1 A.1
Part1 A.2
Part1 A.3
Part1 B.1
Part1 B.2
If you set color="blue" for Part1 B revision then B.1 and B.2 will have color="blue". Likewise, if you set it to "yellow" for the A revision then A.1, A.2 and A.3 will have a value of "yellow."
Note: if you are working with CAD data and these attributes are tied CAD parameters then you have to define the attributes on the CAD Document and not on the CAD Document Master.
I hope that helps!