Parameters with or without 'AS' keyword in TSQL

Question

I'm somewhat new to TSQL (mostly MySQL experience). I came across some parameter declarations and I'm unsure what, if any, the difference is when declared in a stored proc with versus without the 'as' keyword:

CREATE PROCEDURE [dbo].[SomeStoredProc]
    @variable1 varchar(50),
    @variable2 as varchar(50)
...

Answer 1

Strangely enough the documentation does not show AS as being part of the syntax neither optional nor mandatory.

But, anyway, there is no difference.