We have clarified how consumers that do not understand superluminous colors should behave when encountering them in section 11.4.1 of the XPS specification v0.95. The text is as follows:

Consumers MAY handle superluminous colors or MAY instead choose to convert pre-multiplied source data containing superluminous colors to non-pre-multiplied data before composition by ignoring the superluminous portion of each color channel value [O11.10], as described in the following steps:

For each superluminous pixel with A < R or A < G or A < B

{

   If A = 0

   {

      R* = 1

      G* = 1

      B* = 1

   }

   Else

   {

      A* = A

      R* = min(R/A,1)

      G* = min(G/A,1)

      B* = min(B/A,1)

   }

}