Added back the optional pipe before the patterns
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> _MatchArmPatterns_ _MatchArmGuard_
>
> _MatchArmPatterns_ :
-> &nbsp;&nbsp; _Pattern_ ( `|` _Pattern_ )<sup>*</sup>
+> &nbsp;&nbsp; `|`<sup>?</sup> _Pattern_ ( `|` _Pattern_ )<sup>*</sup>
>
> _MatchArmGuard_ :
> &nbsp;&nbsp; `if` [_Expression_]
