diff --git a/lib/kernel/matchers/omega.ml b/lib/kernel/matchers/omega.ml
index bc41c81..1314ca8 100644
--- a/lib/kernel/matchers/omega.ml
+++ b/lib/kernel/matchers/omega.ml
@@ -1015,7 +1015,7 @@ module Make (Language : Types.Language.S) (Meta : Metasyntax.S) = struct
       let rec aux_all ?configuration ?(nested = false) ~template ~source () =
         matches_ref := [];
         if String.is_empty template && String.is_empty source then [trivial]
-        else match first_is_broken template source (Some rule) with (* FIXME always Some rule *)
+        else match first_is_broken template source (Some rule) with
           | Ok _
           | Error _ ->
             let matches = List.rev !matches_ref in
diff --git a/lib/kernel/matchers/rewrite.ml b/lib/kernel/matchers/rewrite.ml
index f4a7d58..e4d5be1 100644
--- a/lib/kernel/matchers/rewrite.ml
+++ b/lib/kernel/matchers/rewrite.ml
@@ -22,12 +22,16 @@ let replacement_sentinel metasyntax =
         let left = Option.value left ~default:"" in
         let right = Option.value right ~default:"" in
         Some (left, right)
+      | Hole (Alphanum, Delimited (left, right)) ->
+        let left = Option.value left ~default:"" in
+        let right = Option.value right ~default:"" in
+        Some (left, right)
       | Regex (left, _, right) ->
         Some (left, right)
       | _ -> None)
   |> function
   | Some v -> v
-  | None -> failwith "A custom metasyntax must define syntax for an Everything hole or Regex to customize rewriting"
+  | None -> failwith "A custom metasyntax must define syntax for an Everything or Alphanum hole or Regex to customize rewriting"
 
 (** Parse the first :[id(label)] label encountered in the template. *)
 let parse_first_label ?(metasyntax = Metasyntax.default_metasyntax) template =
diff --git a/test/common/test_custom_metasyntax.ml b/test/common/test_custom_metasyntax.ml
index 25668e6..82487b7 100644
--- a/test/common/test_custom_metasyntax.ml
+++ b/test/common/test_custom_metasyntax.ml
@@ -1,6 +1,7 @@
 open Core
 
 open Comby_kernel
+open Test_helpers
 
 let configuration = Matchers.Configuration.create ~match_kind:Fuzzy ()
 
@@ -8,12 +9,6 @@ let create (module E : Matchers.Engine.S) syntax =
   let metasyntax = Matchers.Metasyntax.{ syntax; identifier = "ABCDEFGHIJKLMNOPQRSTUVWXYZ_" } in
   Option.value_exn (E.select_with_extension ~metasyntax ".go")
 
-let run (module M : Matchers.Matcher.S) source match_template _rewrite_template =
-  M.all ~configuration ~template:match_template ~source ()
-  |> function
-  | [] -> print_string "No matches."
-  | results -> print_string (Format.asprintf "%a" Match.pp_json_lines (None, results))
-
 let%expect_test "custom_metasyntax_everything" =
   let matcher =
     [ Matchers.Metasyntax.Hole (Everything, Delimited (Some "$", None))
@@ -21,28 +16,28 @@ let%expect_test "custom_metasyntax_everything" =
   in
 
   let source = "simple(test)" in
-  run (create (module Matchers.Alpha) matcher) source "simple($A)" "";
+  run_all_matches (create (module Matchers.Alpha) matcher) source "simple($A)";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":12,"line":1,"column":13}},"environment":[{"variable":"A","value":"test","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}}}],"matched":"simple(test)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) source "simple($A)" "";
+  run_all_matches (create (module Matchers.Omega) matcher) source "simple($A)";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":12,"line":1,"column":13}},"environment":[{"variable":"A","value":"test","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}}}],"matched":"simple(test)"}]}
 |}];
 
 
   let source = "(nested(test))" in
-  run (create (module Matchers.Alpha) matcher) source "($A)" "";
+  run_all_matches (create (module Matchers.Alpha) matcher) source "($A)";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":14,"line":1,"column":15}},"environment":[{"variable":"A","value":"nested(test)","range":{"start":{"offset":1,"line":1,"column":2},"end":{"offset":13,"line":1,"column":14}}}],"matched":"(nested(test))"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) source "($A)" "";
+  run_all_matches (create (module Matchers.Omega) matcher) source "($A)";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":14,"line":1,"column":15}},"environment":[{"variable":"A","value":"nested(test)","range":{"start":{"offset":1,"line":1,"column":2},"end":{"offset":13,"line":1,"column":14}}}],"matched":"(nested(test))"}]}
 |}];
 
 
   let source = "flat stuff yeah" in
-  run (create (module Matchers.Alpha) matcher) source "flat $A yeah" "";
+  run_all_matches (create (module Matchers.Alpha) matcher) source "flat $A yeah";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":15,"line":1,"column":16}},"environment":[{"variable":"A","value":"stuff","range":{"start":{"offset":5,"line":1,"column":6},"end":{"offset":10,"line":1,"column":11}}}],"matched":"flat stuff yeah"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) source "flat $A yeah" "";
+  run_all_matches (create (module Matchers.Omega) matcher) source "flat $A yeah";
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":15,"line":1,"column":16}},"environment":[{"variable":"A","value":"stuff","range":{"start":{"offset":5,"line":1,"column":6},"end":{"offset":10,"line":1,"column":11}}}],"matched":"flat stuff yeah"}]}
 |}]
 
@@ -55,10 +50,10 @@ let%expect_test "custom_metasyntax_regex" =
   in
 
   let source = "simple(test)" in
-  run (create (module Matchers.Alpha) matcher) source {|$A:\w+ |} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) source {|$A:\w+ |};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}}],"matched":"simple"},{"range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"test","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}}}],"matched":"test"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) source {|$A:\w+ |} "";
+  run_all_matches (create (module Matchers.Omega) matcher) source {|$A:\w+ |};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}}],"matched":"simple"},{"range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"test","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":11,"line":1,"column":12}}}],"matched":"test"}]}
 |}]
 
@@ -70,17 +65,17 @@ let%expect_test "custom_metasyntax_multiple_holes" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)" {|$FOO(?BAR)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)" {|$FOO(?BAR)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"BAR","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}},{"variable":"FOO","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}}],"matched":"simple(bar)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "simple(bar)" {|$FOO(?BAR)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)" {|$FOO(?BAR)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"BAR","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}},{"variable":"FOO","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}}],"matched":"simple(bar)"}]}
 |}];
 
-  run (create (module Matchers.Alpha) matcher) "foo(bar)" {|?FOO($BAR)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "foo(bar)" {|?FOO($BAR)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":8,"line":1,"column":9}},"environment":[{"variable":"BAR","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}},{"variable":"FOO","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo(bar)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "foo(bar)" {|?FOO($BAR)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "foo(bar)" {|?FOO($BAR)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":8,"line":1,"column":9}},"environment":[{"variable":"BAR","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}},{"variable":"FOO","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo(bar)"}]}
 |}];
 
@@ -91,10 +86,10 @@ let%expect_test "custom_metasyntax_multiple_holes" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$$A|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$$A|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}},"environment":[{"variable":"A","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo"},{"range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}},"environment":[{"variable":"A","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}}],"matched":"bar"},{"range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"baz","range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}}}],"matched":"baz"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$$A|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$$A|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}},"environment":[{"variable":"A","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo"},{"range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}},"environment":[{"variable":"A","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}}],"matched":"bar"},{"range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"baz","range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}}}],"matched":"baz"}]}
 |}];
 
@@ -106,10 +101,10 @@ let%expect_test "custom_metasyntax_multiple_holes" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$M:\w+ |} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$M:\w+ |};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}},"environment":[{"variable":"M","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo"},{"range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}},"environment":[{"variable":"M","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}}],"matched":"bar"},{"range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"M","value":"baz","range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}}}],"matched":"baz"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$M:\w+ |} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$M:\w+ |};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}},"environment":[{"variable":"M","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo"},{"range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}},"environment":[{"variable":"M","value":"bar","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}}],"matched":"bar"},{"range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"M","value":"baz","range":{"start":{"offset":8,"line":1,"column":9},"end":{"offset":11,"line":1,"column":12}}}],"matched":"baz"}]}
 |}];
 
@@ -122,9 +117,9 @@ let%expect_test "custom_metasyntax_multiple_holes" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$M:\w+ |} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "foo(bar.baz)" {|$M:\w+ |};
   [%expect_exact {|No matches.|}];
-  run (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$M:\w+ |} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "foo(bar.baz)" {|$M:\w+ |};
   [%expect_exact {|No matches.|}]
 
 
@@ -136,11 +131,11 @@ let%expect_test "custom_metasyntax_underscore" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)" {|$_(?_)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)" {|$_(?_)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"_","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}}],"matched":"simple(bar)"}]}
 |}];
   (* different because we record _ the first time and don't subsequently for implicit_equals *)
-  run (create (module Matchers.Omega) matcher) "simple(bar)" {|$_(?_)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)" {|$_(?_)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"_","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}}],"matched":"simple(bar)"}]}
 |}]
 
@@ -152,10 +147,10 @@ let%expect_test "custom_metasyntax_equivalence" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "foo(foo)" {|$A($A~\w+$)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "foo(foo)" {|$A($A~\w+$)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":8,"line":1,"column":9}},"environment":[{"variable":"A","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}},{"variable":"A_equal_!@#$000000000011","value":"foo","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}}],"matched":"foo(foo)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "foo(foo)" {|$A($A~\w+$)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "foo(foo)" {|$A($A~\w+$)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":8,"line":1,"column":9}},"environment":[{"variable":"A","value":"foo","range":{"start":{"offset":4,"line":1,"column":5},"end":{"offset":7,"line":1,"column":8}}},{"variable":"A_equal_!@#$000000000012","value":"foo","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":3,"line":1,"column":4}}}],"matched":"foo(foo)"}]}
 |}]
 
@@ -167,9 +162,9 @@ let%expect_test "custom_metasyntax_definition_order" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|};
   [%expect_exact {|No matches.|}];
-  run (create (module Matchers.Omega) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|};
   [%expect_exact {|No matches.|}];
 
   let matcher =
@@ -179,10 +174,10 @@ let%expect_test "custom_metasyntax_definition_order" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":14,"line":1,"column":15}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"B","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}},{"variable":"C","value":"baz","range":{"start":{"offset":11,"line":1,"column":12},"end":{"offset":14,"line":1,"column":15}}}],"matched":"simple(bar)baz"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)baz" {|$A($B)$C~\w+$|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":14,"line":1,"column":15}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"B","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}},{"variable":"C","value":"baz","range":{"start":{"offset":11,"line":1,"column":12},"end":{"offset":14,"line":1,"column":15}}}],"matched":"simple(bar)baz"}]}
 |}]
 
@@ -253,10 +248,10 @@ let%expect_test "custom_metasyntax_greek_letters" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)" {|α(β)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)" {|α(β)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"α","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"β","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}}],"matched":"simple(bar)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "simple(bar)" {|α(β)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)" {|α(β)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"α","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"β","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}}],"matched":"simple(bar)"}]}
 |}]
 
@@ -268,9 +263,24 @@ let%expect_test "custom_metasyntax_alphanum_test" =
       ]
   in
 
-  run (create (module Matchers.Alpha) matcher) "simple(bar)" {|[:A:](α)|} "";
+  run_all_matches (create (module Matchers.Alpha) matcher) "simple(bar)" {|[:A:](α)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"α","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}}],"matched":"simple(bar)"}]}
 |}];
-  run (create (module Matchers.Omega) matcher) "simple(bar)" {|[:A:](α)|} "";
+  run_all_matches (create (module Matchers.Omega) matcher) "simple(bar)" {|[:A:](α)|};
   [%expect_exact {|{"uri":null,"matches":[{"range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":11,"line":1,"column":12}},"environment":[{"variable":"A","value":"simple","range":{"start":{"offset":0,"line":1,"column":1},"end":{"offset":6,"line":1,"column":7}}},{"variable":"α","value":"bar","range":{"start":{"offset":7,"line":1,"column":8},"end":{"offset":10,"line":1,"column":11}}}],"matched":"simple(bar)"}]}
 |}]
+
+let%expect_test "custom_metasyntax_rewrite_length" =
+  let syntax =
+    Matchers.Metasyntax.
+      [ Hole (Alphanum, Delimited (Some "[:", Some ":]"))
+      ; Hole (Alphanum, Reserved_identifiers ["α"; "β"])
+      ]
+  in
+
+  let metasyntax = Matchers.Metasyntax.{ syntax; identifier = "ABCDEFGHIJKLMNOPQRSTUVWXYZ_" } in
+
+  run ~metasyntax (create (module Matchers.Alpha) syntax) "simple(bar)" {|[:A:](α)|} {|[:A:].length (α.length)|};
+  [%expect_exact {|6 (3)|}];
+  run ~metasyntax (create (module Matchers.Omega) syntax) "simple(bar)" {|[:A:](α)|} {|[:A:].length (α.length)|};
+  [%expect_exact {|6 (3)|}]
diff --git a/test/common/test_helpers.ml b/test/common/test_helpers.ml
index d55c68a..a9be92c 100644
--- a/test/common/test_helpers.ml
+++ b/test/common/test_helpers.ml
@@ -27,7 +27,7 @@ let print_only_match matches =
   |> Yojson.Safe.pretty_to_string
   |> print_string
 
-let run ?(configuration = configuration) (module M : Matchers.Matcher.S) source match_template ?rule rewrite_template =
+let run ?(configuration = configuration) ?metasyntax (module M : Matchers.Matcher.S) source match_template ?rule rewrite_template =
   let rule =
     match rule with
     | Some rule -> Matchers.Rule.create rule |> Or_error.ok_exn
@@ -37,7 +37,7 @@ let run ?(configuration = configuration) (module M : Matchers.Matcher.S) source
   |> function
   | [] -> print_string "No matches."
   | results ->
-    Option.value_exn (Rewrite.all ~source ~rewrite_template results)
+    Option.value_exn (Rewrite.all ?metasyntax ~source ~rewrite_template results)
     |> (fun { rewritten_source; _ } -> rewritten_source)
     |> print_string