what is the difference between AliasAssign and AliasReassignment

[FabArd via Digitalmars-d-learn]

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?