There are three places that I think we should consider marking as "Modified in PrintTalk 2.1":
1) In section 3.7 OrderStatusResponse, the second paragraph is:
If a Print Provider receives an OrderStatusRequest[@Subscribed="false"], it SHALL immediately send to the Print Buyer one OrderStatusResponse with the latest reached milestone for each OrderStatusRequest/StatusRequest.
In the 2.0.1 spec, the word "false" was instead stated as "true". This seems like a fairly significant change to go unmarked.
2) In Table 4.1: Additional Element, the @BaseAmount and @BasePrice attributes both include new statements with "SHALL"s in them:
The value of @BaseAmount SHALL be equal to or higher than the value of a Price[@PriceType="Product"]/@Amount.
The value of @BasePrice SHALL be equal to or higher than the value of the parent Price/@BasePrice.
Adding new requirements might be worth marking?
3) In Table 4.7: Price Element, the @Amount attribute had one "SHALL" changed to another:
From: If @UnitPrice is specified, @Amount SHALL be specified.
To: @Amount SHALL be specified if @PriceType="Product".
The deletion of the first statement was due to the deprecation of the @UnitPrice attribute. The addition of the second statement is a new requirement. Should this be marked?