WHITESPACE = _{ " " }

Rew       = ! { ( ASCII_DIGIT | ASCII_ALPHA_UPPER | "_" | "-" ) + }
Lit       = ! { ( ASCII_ALPHANUMERIC              | "_" | "-" ) + }
Word      = _ { Rew | Lit }
WordGroup = _ { Word ~ ( " " ~ Word ) * }

// Argument groups are nonatomic;
// "<whitespace |between|the|bar|or|braces |is | OK>"

ArgOptChoiceGroup = { ( "[" ~ Word + ~
                      ( "|" ~ ( Word
                              | ArgChoiceGroup ) + ) * ~
                        "]" ) + }
ArgReqChoiceGroup = { ( "<" ~ Word + ~
                      ( "|" ~ ( Word
                              | ArgChoiceGroup ) + ) * ~
                        ">" ) + }
ArgChoiceGroup    = _ { ArgOptChoiceGroup
                      | ArgReqChoiceGroup }

Command = {
    ( WordGroup ) ~
    ( ArgChoiceGroup ) *
}

HelpMenu = {
    SOI ~

    (
        Command ~
        NEWLINE
    ) * ~

    EOI
}