Attribute 0 is forbidden
Oh well

Revert "Attribute codes of zero are forbidden"

This reverts commit 12da0d625f0bd5f35c6887e9050eeb189329ca27.
Revert "Attribute 0 is forbidden"

This reverts commit d5b6011a6ffb27c48a12b694bb9cfcfc0f7c5466.