There are problems with the EBNF on the sudoers man page.

Without loss of generality, I'll describe the problem with the User_Alias symbol, but analogous problems exist for all aliases.

The production for the User_Alias symbol makes it clear that the symbol represents the *definition* of a user alias, not the *name* for a user alias...

    User_Alias ::= NAME ’=’ User_List

But then the symbol "User_Alias" is used in several contexts where it is clear that what is intended is the *name* for the user alias, not the *definition* of the user alias, e.g. ...

    User ::= ’!’* user name |
             ’!’* #uid |
             ’!’* %group |
             ’!’* %#gid |
             ’!’* +netgroup |
             ’!’* %:nonunix_group |
             ’!’* %:#nonunix_gid |
             ’!’* User_Alias

It would appear that another production is needed, perhaps something like...

    User_Alias_Name ::= NAME

And the new symbol "User_Alias_Name" could be used the fix the problem.  The production for User_Alias would become...

    User_Alias ::= User_Alias_Name '=' User_List

And then every reference to the "User_Alias" symbol -- except for the one use in the production for the "Alias" symbol -- would be changed to "User_Alias_Name".

Or, if you prefer, you could continue using the symbol "User_Alias" to represent the name, but change the symbol used for the alias definition...

    User_Alias ::= NAME
    User_Alias_Definition ::= NAME ’=’ User_List

    <Then change the "Alias" production to use "User_Alias_Definition">

I think I might like this alternative best.  But you decide.