what is the difference between AliasAssign and AliasReassignment

[FabArd]

Hi,

I don't understand a point in the grammar :

     5.4.6 AliasAssign:
         Identifier = Type

     5.4.7 AliasReassignment:
         Identifier = StorageClasses(optional) Type

AliasAssign rule is included in the AliasReassignment rule.

Why there are two rules in the grammar to describe the same thing?