varchar(max) in FK constraint? CREATE TABLE topic on BOL by Martin Smith

From http://msdn.microsoft.com/en-us/library/ms174979.aspx

"A column of type varchar(max) can participate in a FOREIGN KEY constraint only if the primary key it references is also defined as type varchar(max)."

Well I suppose technically it is correct but AFAIK it is not possible to create a PK with such a column so this can never arise.

I presume that this is intended to make the point that the length of varchar columns must be the same on both sides of the relationship.