yang-grammer-0.abnf

12.  YANG ABNF Grammar

   In YANG, almost all statements are unordered.  The ABNF grammar
   [RFC5234] defines the canonical order.  To improve module
   readability, it is RECOMMENDED that clauses be entered in this order.

   Within the ABNF grammar, unordered statements are marked with
   comments.

   This grammar assumes that the scanner replaces YANG comments with a
   single space character.

   <CODE BEGINS> file "yang.abnf"

   module-stmt         = optsep module-keyword sep identifier-arg-str
                         optsep
                         "{" stmtsep
                             module-header-stmts
                             linkage-stmts
                             meta-stmts
                             revision-stmts
                             body-stmts
                         "}" optsep

   submodule-stmt      = optsep submodule-keyword sep identifier-arg-str
                         optsep
                         "{" stmtsep
                             submodule-header-stmts
                             linkage-stmts
                             meta-stmts
                             revision-stmts
                             body-stmts
                         "}" optsep

   module-header-stmts = ;; these stmts can appear in any order
                         [yang-version-stmt stmtsep]
                          namespace-stmt stmtsep
                          prefix-stmt stmtsep

   submodule-header-stmts =
                         ;; these stmts can appear in any order
                         [yang-version-stmt stmtsep]
                          belongs-to-stmt stmtsep








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RFC 6020                          YANG                      October 2010


   meta-stmts          = ;; these stmts can appear in any order
                         [organization-stmt stmtsep]
                         [contact-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   linkage-stmts       = ;; these stmts can appear in any order
                         *(import-stmt stmtsep)
                         *(include-stmt stmtsep)

   revision-stmts      = *(revision-stmt stmtsep)

   body-stmts          = *((extension-stmt /
                            feature-stmt /
                            identity-stmt /
                            typedef-stmt /
                            grouping-stmt /
                            data-def-stmt /
                            augment-stmt /
                            rpc-stmt /
                            notification-stmt /
                            deviation-stmt) stmtsep)

   data-def-stmt       = container-stmt /
                         leaf-stmt /
                         leaf-list-stmt /
                         list-stmt /
                         choice-stmt /
                         anyxml-stmt /
                         uses-stmt

   yang-version-stmt   = yang-version-keyword sep yang-version-arg-str
                         optsep stmtend

   yang-version-arg-str = < a string that matches the rule
                           yang-version-arg >

   yang-version-arg    = "1"

   import-stmt         = import-keyword sep identifier-arg-str optsep
                         "{" stmtsep
                             prefix-stmt stmtsep
                             [revision-date-stmt stmtsep]
                         "}"







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RFC 6020                          YANG                      October 2010


   include-stmt        = include-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              [revision-date-stmt stmtsep]
                          "}")

   namespace-stmt      = namespace-keyword sep uri-str optsep stmtend

   uri-str             = < a string that matches the rule
                           URI in RFC 3986 >

   prefix-stmt         = prefix-keyword sep prefix-arg-str
                         optsep stmtend

   belongs-to-stmt     = belongs-to-keyword sep identifier-arg-str
                         optsep
                         "{" stmtsep
                             prefix-stmt stmtsep
                         "}"

   organization-stmt   = organization-keyword sep string
                         optsep stmtend

   contact-stmt        = contact-keyword sep string optsep stmtend

   description-stmt    = description-keyword sep string optsep
                         stmtend

   reference-stmt      = reference-keyword sep string optsep stmtend

   units-stmt          = units-keyword sep string optsep stmtend

   revision-stmt       = revision-keyword sep revision-date optsep
                         (";" /
                          "{" stmtsep
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                          "}")

   revision-date       =  date-arg-str

   revision-date-stmt = revision-date-keyword sep revision-date stmtend









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RFC 6020                          YANG                      October 2010


   extension-stmt      = extension-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [argument-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                          "}")

   argument-stmt       = argument-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              [yin-element-stmt stmtsep]
                          "}")

   yin-element-stmt    = yin-element-keyword sep yin-element-arg-str
                         stmtend

   yin-element-arg-str = < a string that matches the rule
                           yin-element-arg >

   yin-element-arg     = true-keyword / false-keyword

   identity-stmt       = identity-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [base-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                          "}")

   base-stmt           = base-keyword sep identifier-ref-arg-str
                         optsep stmtend

   feature-stmt        = feature-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              *(if-feature-stmt stmtsep)
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                          "}")





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RFC 6020                          YANG                      October 2010


   if-feature-stmt     = if-feature-keyword sep identifier-ref-arg-str
                         optsep stmtend

   typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             type-stmt stmtsep
                             [units-stmt stmtsep]
                             [default-stmt stmtsep]
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                          "}"

   type-stmt           = type-keyword sep identifier-ref-arg-str optsep
                         (";" /
                          "{" stmtsep
                              type-body-stmts
                          "}")

   type-body-stmts     = numerical-restrictions /
                         decimal64-specification /
                         string-restrictions /
                         enum-specification /
                         leafref-specification /
                         identityref-specification /
                         instance-identifier-specification /
                         bits-specification /
                         union-specification

   numerical-restrictions = range-stmt stmtsep

   range-stmt          = range-keyword sep range-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [error-message-stmt stmtsep]
                              [error-app-tag-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   decimal64-specification = fraction-digits-stmt

   fraction-digits-stmt = fraction-digits-keyword sep
                          fraction-digits-arg-str stmtend





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RFC 6020                          YANG                      October 2010


   fraction-digits-arg-str = < a string that matches the rule
                              fraction-digits-arg >

   fraction-digits-arg = ("1" ["0" / "1" / "2" / "3" / "4" /
                               "5" / "6" / "7" / "8"])
                         / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"

   string-restrictions = ;; these stmts can appear in any order
                         [length-stmt stmtsep]
                         *(pattern-stmt stmtsep)

   length-stmt         = length-keyword sep length-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [error-message-stmt stmtsep]
                              [error-app-tag-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   pattern-stmt        = pattern-keyword sep string optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [error-message-stmt stmtsep]
                              [error-app-tag-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   default-stmt        = default-keyword sep string stmtend

   enum-specification  = 1*(enum-stmt stmtsep)

   enum-stmt           = enum-keyword sep string optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [value-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")







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RFC 6020                          YANG                      October 2010


   leafref-specification =
                         ;; these stmts can appear in any order
                         path-stmt stmtsep
                         [require-instance-stmt stmtsep]

   path-stmt           = path-keyword sep path-arg-str stmtend

   require-instance-stmt = require-instance-keyword sep
                            require-instance-arg-str stmtend

   require-instance-arg-str = < a string that matches the rule
                              require-instance-arg >

   require-instance-arg = true-keyword / false-keyword


   instance-identifier-specification =
                         [require-instance-stmt stmtsep]

   identityref-specification =
                         base-stmt stmtsep

   union-specification = 1*(type-stmt stmtsep)

   bits-specification  = 1*(bit-stmt stmtsep)

   bit-stmt            = bit-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [position-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                            "}"
                          "}")

   position-stmt       = position-keyword sep
                         position-value-arg-str stmtend

   position-value-arg-str = < a string that matches the rule
                              position-value-arg >

   position-value-arg  = non-negative-integer-value

   status-stmt         = status-keyword sep status-arg-str stmtend





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RFC 6020                          YANG                      October 2010


   status-arg-str      = < a string that matches the rule
                           status-arg >

   status-arg          = current-keyword /
                         obsolete-keyword /
                         deprecated-keyword

   config-stmt         = config-keyword sep
                         config-arg-str stmtend

   config-arg-str      = < a string that matches the rule
                           config-arg >

   config-arg          = true-keyword / false-keyword

   mandatory-stmt      = mandatory-keyword sep
                         mandatory-arg-str stmtend

   mandatory-arg-str   = < a string that matches the rule
                           mandatory-arg >

   mandatory-arg       = true-keyword / false-keyword

   presence-stmt       = presence-keyword sep string stmtend

   ordered-by-stmt     = ordered-by-keyword sep
                         ordered-by-arg-str stmtend

   ordered-by-arg-str  = < a string that matches the rule
                           ordered-by-arg >

   ordered-by-arg      = user-keyword / system-keyword

   must-stmt           = must-keyword sep string optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [error-message-stmt stmtsep]
                              [error-app-tag-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   error-message-stmt  = error-message-keyword sep string stmtend

   error-app-tag-stmt  = error-app-tag-keyword sep string stmtend





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RFC 6020                          YANG                      October 2010


   min-elements-stmt   = min-elements-keyword sep
                         min-value-arg-str stmtend

   min-value-arg-str   = < a string that matches the rule
                           min-value-arg >

   min-value-arg       = non-negative-integer-value

   max-elements-stmt   = max-elements-keyword sep
                         max-value-arg-str stmtend

   max-value-arg-str   = < a string that matches the rule
                           max-value-arg >

   max-value-arg       = unbounded-keyword /
                         positive-integer-value

   value-stmt          = value-keyword sep integer-value stmtend

   grouping-stmt       = grouping-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *((typedef-stmt /
                                 grouping-stmt) stmtsep)
                              *(data-def-stmt stmtsep)
                          "}")

   container-stmt      = container-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [when-stmt stmtsep]
                              *(if-feature-stmt stmtsep)
                              *(must-stmt stmtsep)
                              [presence-stmt stmtsep]
                              [config-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *((typedef-stmt /
                                 grouping-stmt) stmtsep)
                              *(data-def-stmt stmtsep)
                          "}")




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RFC 6020                          YANG                      October 2010


   leaf-stmt           = leaf-keyword sep identifier-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [when-stmt stmtsep]
                             *(if-feature-stmt stmtsep)
                             type-stmt stmtsep
                             [units-stmt stmtsep]
                             *(must-stmt stmtsep)
                             [default-stmt stmtsep]
                             [config-stmt stmtsep]
                             [mandatory-stmt stmtsep]
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                          "}"

   leaf-list-stmt      = leaf-list-keyword sep identifier-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [when-stmt stmtsep]
                             *(if-feature-stmt stmtsep)
                             type-stmt stmtsep
                             [units-stmt stmtsep]
                             *(must-stmt stmtsep)
                             [config-stmt stmtsep]
                             [min-elements-stmt stmtsep]
                             [max-elements-stmt stmtsep]
                             [ordered-by-stmt stmtsep]
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                          "}"

   list-stmt           = list-keyword sep identifier-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [when-stmt stmtsep]
                             *(if-feature-stmt stmtsep)
                             *(must-stmt stmtsep)
                             [key-stmt stmtsep]
                             *(unique-stmt stmtsep)
                             [config-stmt stmtsep]
                             [min-elements-stmt stmtsep]
                             [max-elements-stmt stmtsep]
                             [ordered-by-stmt stmtsep]
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]



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RFC 6020                          YANG                      October 2010


                             *((typedef-stmt /
                                grouping-stmt) stmtsep)
                             1*(data-def-stmt stmtsep)
                          "}"

   key-stmt            = key-keyword sep key-arg-str stmtend

   key-arg-str         = < a string that matches the rule
                           key-arg >

   key-arg             = node-identifier *(sep node-identifier)

   unique-stmt         = unique-keyword sep unique-arg-str stmtend

   unique-arg-str      = < a string that matches the rule
                           unique-arg >

   unique-arg          = descendant-schema-nodeid
                         *(sep descendant-schema-nodeid)

   choice-stmt         = choice-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [when-stmt stmtsep]
                              *(if-feature-stmt stmtsep)
                              [default-stmt stmtsep]
                              [config-stmt stmtsep]
                              [mandatory-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *((short-case-stmt / case-stmt) stmtsep)
                          "}")

   short-case-stmt     = container-stmt /
                         leaf-stmt /
                         leaf-list-stmt /
                         list-stmt /
                         anyxml-stmt

   case-stmt           = case-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [when-stmt stmtsep]
                              *(if-feature-stmt stmtsep)
                              [status-stmt stmtsep]



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RFC 6020                          YANG                      October 2010


                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *(data-def-stmt stmtsep)
                          "}")

   anyxml-stmt         = anyxml-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [when-stmt stmtsep]
                              *(if-feature-stmt stmtsep)
                              *(must-stmt stmtsep)
                              [config-stmt stmtsep]
                              [mandatory-stmt stmtsep]
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   uses-stmt           = uses-keyword sep identifier-ref-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              [when-stmt stmtsep]
                              *(if-feature-stmt stmtsep)
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *(refine-stmt stmtsep)
                              *(uses-augment-stmt stmtsep)
                          "}")

   refine-stmt         = refine-keyword sep refine-arg-str optsep
                         (";" /
                          "{" stmtsep
                              (refine-container-stmts /
                               refine-leaf-stmts /
                               refine-leaf-list-stmts /
                               refine-list-stmts /
                               refine-choice-stmts /
                               refine-case-stmts /
                               refine-anyxml-stmts)
                          "}")

   refine-arg-str      = < a string that matches the rule
                           refine-arg >

   refine-arg          = descendant-schema-nodeid



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RFC 6020                          YANG                      October 2010


   refine-container-stmts =
                         ;; these stmts can appear in any order
                         *(must-stmt stmtsep)
                         [presence-stmt stmtsep]
                         [config-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   refine-leaf-stmts   = ;; these stmts can appear in any order
                         *(must-stmt stmtsep)
                         [default-stmt stmtsep]
                         [config-stmt stmtsep]
                         [mandatory-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   refine-leaf-list-stmts =
                         ;; these stmts can appear in any order
                         *(must-stmt stmtsep)
                         [config-stmt stmtsep]
                         [min-elements-stmt stmtsep]
                         [max-elements-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   refine-list-stmts   = ;; these stmts can appear in any order
                         *(must-stmt stmtsep)
                         [config-stmt stmtsep]
                         [min-elements-stmt stmtsep]
                         [max-elements-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   refine-choice-stmts = ;; these stmts can appear in any order
                         [default-stmt stmtsep]
                         [config-stmt stmtsep]
                         [mandatory-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   refine-case-stmts   = ;; these stmts can appear in any order
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]


   refine-anyxml-stmts = ;; these stmts can appear in any order
                         *(must-stmt stmtsep)
                         [config-stmt stmtsep]



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RFC 6020                          YANG                      October 2010


                         [mandatory-stmt stmtsep]
                         [description-stmt stmtsep]
                         [reference-stmt stmtsep]

   uses-augment-stmt   = augment-keyword sep uses-augment-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [when-stmt stmtsep]
                             *(if-feature-stmt stmtsep)
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                             1*((data-def-stmt stmtsep) /
                                (case-stmt stmtsep))
                          "}"

   uses-augment-arg-str = < a string that matches the rule
                            uses-augment-arg >

   uses-augment-arg    = descendant-schema-nodeid

   augment-stmt        = augment-keyword sep augment-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [when-stmt stmtsep]
                             *(if-feature-stmt stmtsep)
                             [status-stmt stmtsep]
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                             1*((data-def-stmt stmtsep) /
                                (case-stmt stmtsep))
                          "}"

   augment-arg-str     = < a string that matches the rule
                           augment-arg >

   augment-arg         = absolute-schema-nodeid

   unknown-statement   = prefix ":" identifier [sep string] optsep
                         (";" / "{" *unknown-statement2 "}")

   unknown-statement2   = [prefix ":"] identifier [sep string] optsep
                         (";" / "{" *unknown-statement2 "}")

   when-stmt           = when-keyword sep string optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order



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RFC 6020                          YANG                      October 2010


                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                           "}")

   rpc-stmt            = rpc-keyword sep identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              *(if-feature-stmt stmtsep)
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *((typedef-stmt /
                                 grouping-stmt) stmtsep)
                              [input-stmt stmtsep]
                              [output-stmt stmtsep]
                          "}")

   input-stmt          = input-keyword optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             *((typedef-stmt /
                                grouping-stmt) stmtsep)
                             1*(data-def-stmt stmtsep)
                         "}"

   output-stmt         = output-keyword optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             *((typedef-stmt /
                                grouping-stmt) stmtsep)
                             1*(data-def-stmt stmtsep)
                         "}"

   notification-stmt   = notification-keyword sep
                         identifier-arg-str optsep
                         (";" /
                          "{" stmtsep
                              ;; these stmts can appear in any order
                              *(if-feature-stmt stmtsep)
                              [status-stmt stmtsep]
                              [description-stmt stmtsep]
                              [reference-stmt stmtsep]
                              *((typedef-stmt /
                                 grouping-stmt) stmtsep)
                              *(data-def-stmt stmtsep)
                          "}")




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RFC 6020                          YANG                      October 2010


   deviation-stmt      = deviation-keyword sep
                         deviation-arg-str optsep
                         "{" stmtsep
                             ;; these stmts can appear in any order
                             [description-stmt stmtsep]
                             [reference-stmt stmtsep]
                             (deviate-not-supported-stmt /
                               1*(deviate-add-stmt /
                                  deviate-replace-stmt /
                                  deviate-delete-stmt))
                         "}"

   deviation-arg-str   = < a string that matches the rule
                           deviation-arg >

   deviation-arg       = absolute-schema-nodeid

   deviate-not-supported-stmt =
                         deviate-keyword sep
                         not-supported-keyword optsep
                         (";" /
                          "{" stmtsep
                          "}")

   deviate-add-stmt    = deviate-keyword sep add-keyword optsep
                         (";" /
                          "{" stmtsep
                              [units-stmt stmtsep]
                              *(must-stmt stmtsep)
                              *(unique-stmt stmtsep)
                              [default-stmt stmtsep]
                              [config-stmt stmtsep]
                              [mandatory-stmt stmtsep]
                              [min-elements-stmt stmtsep]
                              [max-elements-stmt stmtsep]
                          "}")

   deviate-delete-stmt = deviate-keyword sep delete-keyword optsep
                         (";" /
                          "{" stmtsep
                              [units-stmt stmtsep]
                              *(must-stmt stmtsep)
                              *(unique-stmt stmtsep)
                              [default-stmt stmtsep]
                          "}")






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RFC 6020                          YANG                      October 2010


   deviate-replace-stmt = deviate-keyword sep replace-keyword optsep
                         (";" /
                          "{" stmtsep
                              [type-stmt stmtsep]
                              [units-stmt stmtsep]
                              [default-stmt stmtsep]
                              [config-stmt stmtsep]
                              [mandatory-stmt stmtsep]
                              [min-elements-stmt stmtsep]
                              [max-elements-stmt stmtsep]
                          "}")

   ;; Ranges

   range-arg-str       = < a string that matches the rule
                           range-arg >

   range-arg           = range-part *(optsep "|" optsep range-part)

   range-part          = range-boundary
                         [optsep ".." optsep range-boundary]

   range-boundary      = min-keyword / max-keyword /
                         integer-value / decimal-value

   ;; Lengths

   length-arg-str      = < a string that matches the rule
                           length-arg >

   length-arg          = length-part *(optsep "|" optsep length-part)

   length-part         = length-boundary
                         [optsep ".." optsep length-boundary]

   length-boundary     = min-keyword / max-keyword /
                         non-negative-integer-value

   ;; Date

   date-arg-str        = < a string that matches the rule
                           date-arg >

   date-arg            = 4DIGIT "-" 2DIGIT "-" 2DIGIT







Bjorklund                    Standards Track                  [Page 159]
 
RFC 6020                          YANG                      October 2010


   ;; Schema Node Identifiers

   schema-nodeid       = absolute-schema-nodeid /
                         descendant-schema-nodeid

   absolute-schema-nodeid = 1*("/" node-identifier)

   descendant-schema-nodeid =
                         node-identifier
                         absolute-schema-nodeid

   node-identifier     = [prefix ":"] identifier


   ;; Instance Identifiers

   instance-identifier = 1*("/" (node-identifier *predicate))

   predicate           = "[" *WSP (predicate-expr / pos) *WSP "]"

   predicate-expr      = (node-identifier / ".") *WSP "=" *WSP
                         ((DQUOTE string DQUOTE) /
                          (SQUOTE string SQUOTE))

   pos                 = non-negative-integer-value

   ;; leafref path

   path-arg-str        = < a string that matches the rule
                           path-arg >

   path-arg            = absolute-path / relative-path

   absolute-path       = 1*("/" (node-identifier *path-predicate))

   relative-path       = 1*(".." "/") descendant-path

   descendant-path     = node-identifier
                         [*path-predicate absolute-path]

   path-predicate      = "[" *WSP path-equality-expr *WSP "]"

   path-equality-expr  = node-identifier *WSP "=" *WSP path-key-expr

   path-key-expr       = current-function-invocation *WSP "/" *WSP
                         rel-path-keyexpr





Bjorklund                    Standards Track                  [Page 160]
 
RFC 6020                          YANG                      October 2010


   rel-path-keyexpr    = 1*(".." *WSP "/" *WSP)
                         *(node-identifier *WSP "/" *WSP)
                         node-identifier

   ;;; Keywords, using abnfgen's syntax for case-sensitive strings

   ;; statement keywords
   anyxml-keyword      = 'anyxml'
   argument-keyword    = 'argument'
   augment-keyword     = 'augment'
   base-keyword        = 'base'
   belongs-to-keyword  = 'belongs-to'
   bit-keyword         = 'bit'
   case-keyword        = 'case'
   choice-keyword      = 'choice'
   config-keyword      = 'config'
   contact-keyword     = 'contact'
   container-keyword   = 'container'
   default-keyword     = 'default'
   description-keyword = 'description'
   enum-keyword        = 'enum'
   error-app-tag-keyword = 'error-app-tag'
   error-message-keyword = 'error-message'
   extension-keyword   = 'extension'
   deviation-keyword   = 'deviation'
   deviate-keyword     = 'deviate'
   feature-keyword     = 'feature'
   fraction-digits-keyword = 'fraction-digits'
   grouping-keyword    = 'grouping'
   identity-keyword    = 'identity'
   if-feature-keyword  = 'if-feature'
   import-keyword      = 'import'
   include-keyword     = 'include'
   input-keyword       = 'input'
   key-keyword         = 'key'
   leaf-keyword        = 'leaf'
   leaf-list-keyword   = 'leaf-list'
   length-keyword      = 'length'
   list-keyword        = 'list'
   mandatory-keyword   = 'mandatory'
   max-elements-keyword = 'max-elements'
   min-elements-keyword = 'min-elements'
   module-keyword      = 'module'
   must-keyword        = 'must'
   namespace-keyword   = 'namespace'
   notification-keyword= 'notification'
   ordered-by-keyword  = 'ordered-by'
   organization-keyword= 'organization'



Bjorklund                    Standards Track                  [Page 161]
 
RFC 6020                          YANG                      October 2010


   output-keyword      = 'output'
   path-keyword        = 'path'
   pattern-keyword     = 'pattern'
   position-keyword    = 'position'
   prefix-keyword      = 'prefix'
   presence-keyword    = 'presence'
   range-keyword       = 'range'
   reference-keyword   = 'reference'
   refine-keyword      = 'refine'
   require-instance-keyword = 'require-instance'
   revision-keyword    = 'revision'
   revision-date-keyword = 'revision-date'
   rpc-keyword         = 'rpc'
   status-keyword      = 'status'
   submodule-keyword   = 'submodule'
   type-keyword        = 'type'
   typedef-keyword     = 'typedef'
   unique-keyword      = 'unique'
   units-keyword       = 'units'
   uses-keyword        = 'uses'
   value-keyword       = 'value'
   when-keyword        = 'when'
   yang-version-keyword= 'yang-version'
   yin-element-keyword = 'yin-element'

   ;; other keywords

   add-keyword         = 'add'
   current-keyword     = 'current'
   delete-keyword      = 'delete'
   deprecated-keyword  = 'deprecated'
   false-keyword       = 'false'
   max-keyword         = 'max'
   min-keyword         = 'min'
   not-supported-keyword = 'not-supported'
   obsolete-keyword    = 'obsolete'
   replace-keyword     = 'replace'
   system-keyword      = 'system'
   true-keyword        = 'true'
   unbounded-keyword   = 'unbounded'
   user-keyword        = 'user'










Bjorklund                    Standards Track                  [Page 162]
 
RFC 6020                          YANG                      October 2010


   current-function-invocation = current-keyword *WSP "(" *WSP ")"

   ;; Basic Rules

   prefix-arg-str      = < a string that matches the rule
                           prefix-arg >

   prefix-arg          = prefix

   prefix              = identifier

   identifier-arg-str  = < a string that matches the rule
                           identifier-arg >

   identifier-arg      = identifier

   ;; An identifier MUST NOT start with (('X'|'x') ('M'|'m') ('L'|'l'))
   identifier          = (ALPHA / "_")
                         *(ALPHA / DIGIT / "_" / "-" / ".")

   identifier-ref-arg-str = < a string that matches the rule
                           identifier-ref-arg >

   identifier-ref-arg  = [prefix ":"] identifier

   string              = < an unquoted string as returned by
                           the scanner >

   integer-value       = ("-" non-negative-integer-value)  /
                          non-negative-integer-value

   non-negative-integer-value = "0" / positive-integer-value

   positive-integer-value = (non-zero-digit *DIGIT)

   zero-integer-value  = 1*DIGIT

   stmtend             = ";" / "{" *unknown-statement "}"

   sep                 = 1*(WSP / line-break)
                         ; unconditional separator

   optsep              = *(WSP / line-break)

   stmtsep             = *(WSP / line-break / unknown-statement)

   line-break          = CRLF / LF




Bjorklund                    Standards Track                  [Page 163]
 
RFC 6020                          YANG                      October 2010


   non-zero-digit      = %x31-39

   decimal-value       = integer-value ("." zero-integer-value)

   SQUOTE              = %x27
                         ; ' (Single Quote)

   ;;
   ;; RFC 5234 core rules.
   ;;

   ALPHA               = %x41-5A / %x61-7A
                         ; A-Z / a-z

   CR                  = %x0D
                         ; carriage return

   CRLF                = CR LF
                         ; Internet standard new line

   DIGIT               = %x30-39
                         ; 0-9

   DQUOTE              = %x22
                         ; " (Double Quote)

   HEXDIG              = DIGIT /
                         %x61 / %x62 / %x63 / %x64 / %x65 / %x66
                         ; only lower-case a..f

   HTAB                = %x09
                         ; horizontal tab

   LF                  = %x0A
                         ; linefeed

   SP                  = %x20
                         ; space

   VCHAR               = %x21-7E
                         ; visible (printing) characters

   WSP                 = SP / HTAB
                         ; whitespace

   <CODE ENDS>