diff --git a/src/Internal/Tools/Grammar.elm b/src/Internal/Tools/Grammar.elm
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+module Internal.Tools.Grammar exposing (..)
+
+{-|
+
+
+# Identifier Grammar
+
+The specification defines
+[some identifiers](https://spec.matrix.org/v1.9/appendices/#identifier-grammar)
+to use the Common Namespaced Identifier Grammar. This is a common grammar
+intended for non-user-visible identifiers, with a defined mechanism for
+implementations to create new identifiers.
+
+This module documents those identifiers, allowing the Elm SDK to use them.
+
+-}
+
+import Parser as P exposing (Parser)
+
+
+{-| Parse an IPv6 address
+-}
+ipv6addressParser : Parser String
+ipv6addressParser =
+    P.chompWhile validIPv6Char
+        |> P.getChompedString
+        |> P.andThen
+            (\out ->
+                if String.length out > 45 then
+                    P.problem "an ipv6 address has no more than 45 digits"
+
+                else if String.length out < 2 then
+                    P.problem "an ipv6 address has at least 2 digits"
+
+                else
+                    -- TODO: ipv6 has more specific rules
+                    -- https://datatracker.ietf.org/doc/html/rfc3513#section-2.2
+                    P.succeed out
+            )
+
+
+{-| Parse a port value
+-}
+portParser : Parser Int
+portParser =
+    P.chompWhile Char.isDigit
+        |> P.getChompedString
+        |> P.andThen
+            (\out ->
+                if String.length out > 5 then
+                    P.problem "a port has no more than 5 digits"
+
+                else if String.length out < 1 then
+                    P.problem "a port has at least 1 digit"
+
+                else
+                    case String.toInt out of
+                        Nothing ->
+                            P.problem "Expected port int"
+
+                        Just i ->
+                            P.succeed i
+            )
+
+
+{-| Check whether a char is a valid IPv6char
+-}
+validIPv6char : Char -> Bool
+
+
+validIPv6Char c =
+    "0123456789ABCDEFabcdef:."
+        |> String.toList
+        |> List.member c