(** Message output formatters.

    This module provides various output formats for validation messages,
    including text, JSON, and GNU-style formats for IDE integration. *)

(** {1 Formatters} *)

(** Format messages as human-readable text.

    Output format: [file:line:col: severity: message]

    @param system_id Optional default system identifier for messages without location. *)
val format_text : ?system_id:string -> Message.t list -> string

(** Format messages as JSON.

    Produces output compatible with the Nu HTML Validator JSON format.

    @param system_id Optional default system identifier for messages without location. *)
val format_json : ?system_id:string -> Message.t list -> string

(** Format messages in GNU style for IDE integration.

    Output format follows GNU conventions for error messages, compatible
    with most IDEs and editors.

    @param system_id Optional default system identifier for messages without location. *)
val format_gnu : ?system_id:string -> Message.t list -> string