IS vs AS keywords for PL/SQL Oracle Function or Procedure Creation [duplicate]

I have been trying to find out what the difference is between the IS and AS keywords in PL/SQL when creating an Oracle function or procedure.

I have searched and have been unable to find any information on this. Does anyone know the difference?

I've never known there to be a difference. The Oracle documentation implies that they are synonyms:

The function body begins with the keyword IS (or AS) and ends with the keyword END followed by an optional function name.

Same as DISTINCT and UNIQUE in select statements. i.e, there is no material difference between 'IS' and 'AS'. Backwards compatibility and meeting standards