Clarify right owner for public domain

Author: niemela

spec/2023-07-draft.md

@@ -323,9 +323,11 @@ Value           | Comments
 ### Rights Owner
 
 A rights owner is needed if the [license](#license) is anything other than `unknown` or `public domain`.
+If `license` is `public domain` there is no rights owner and `rights_owner` must not be set.
+
 If `rights_owner` is provided, this is the rights owner.
 Otherwise, if one or several authors are specified in `credits`, that group or individual is the rights owner.
-Otherwise, if a `source` is specified, the legal entity owning the rights associated with that source is the rights owner. 
+Otherwise, if a `source` is specified, the legal entity owning the rights associated with that source is the rights owner.
 
 ### Problem Publication Embargo
 

spec/legacy-icpc.md

@@ -157,8 +157,9 @@ Value           | Comments
 `permission`    | Used with permission. The rights owner must be contacted for every additional use. |
 
 `rights_owner` is the owner of the copyright of the problem.
-Values other than `unknown` or `public domain` require `rights_owner` to have a value.
-`rights_owner` defaults to `credits.authors`, if present, otherwise value of `source`.
+If `license` is not `unknown` or `public domain`, `rights_owner` is required to have a value.
+If `license` is `public domain`, `rights_owner` must not be set.
+`rights_owner` defaults to `credits.authors`, if present, otherwise the value of `source`, otherwise it will have no value.
 
 ### Limits
 

spec/legacy.md

@@ -169,8 +169,9 @@ Value           | Comments
 `permission`    | Used with permission. The rights owner must be contacted for every additional use. |
 
 `rights_owner` is the owner of the copyright of the problem.
-Values other than `unknown` or `public domain` require `rights_owner` to have a value.
-`rights_owner` defaults to `credits.authors`, if present, otherwise value of `source`.
+If `license` is not `unknown` or `public domain`, `rights_owner` is required to have a value.
+If `license` is `public domain`, `rights_owner` must not be set.
+`rights_owner` defaults to `credits.authors`, if present, otherwise the value of `source`, otherwise it will have no value.
 
 ### Limits