Grammar to guide revision

[ggbetz]

Consider providing grammars in tasks that guide revision step. E.g., for infreco:

    start: code_fence_begin (argument_head _NL _NL+)? argument_body code_fence_end
    code_fence_begin: "```argdown" _NL
    code_fence_end: _NL "```"
    argument_head: ARGUMENT_LABEL [":" TEXT]
    argument_body: premise (_NL premise | _NL conclusion)*
    premise: PCS_LABEL _proposition
    conclusion: (INFERENCE_INFO) PCS_LABEL _proposition
    _proposition: (PROPOSITION_LABEL | PROPOSITION_LABEL ":" TEXT | TEXT)

    ARGUMENT_LABEL: "<" /[^\>]+/ ">"
    PROPOSITION_LABEL: "[" /[^\]]+/ "]"
    PCS_LABEL: "(" /[A-Z]?\d+/ ") "
    TEXT: /([^\n]+)/
    INFERENCE_INFO: "-- {'from': " ILIST "} --\n"
    ILIST: "[" IITEM ("," IITEM)* "]" 
    IITEM: "'" /[A-Z]?\d+/ "'"

    %import common.WS_INLINE
    %ignore WS_INLINE

    _NL: /(\r?\n[\t ]*)/