panglesd · panglesd · Feb 16, 2026 · Feb 17, 2026 · Feb 17, 2026 · Feb 17, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Added
+
+- Helpful warnings at compile-time (#213)
+
 ## [v0.9.0] Manim Black (Tuesday 19th February, 2026)
 
 ### Added

diff --git a/docs/_ext/slipshowexample.py b/docs/_ext/slipshowexample.py
@@ -41,6 +41,7 @@ def visit_slipshow_example_node_html(self, node):
     <div class="editor-preview-container">
       <div class="editor"></div>
       <div class="preview"></div>
+      <pre class="errors-el" style="background:black; margin:0; color: white; overflow-y:scroll"></pre>
     </div>
     <div class="source" style="display:none">""")
     # Write raw, *escaped* text so it appears exactly as typed

diff --git a/docs/_static/style.css b/docs/_static/style.css
@@ -1,16 +1,3 @@
-.right-panel1.active_panel, .right-panel2.active_panel {
-  z-index: 1;
-}
-.right-panel1, .right-panel2 {
-    z-index: 0;
-    width:100%;
-    position:absolute;
-    top:0;
-    bottom:0;
-    left:0;
-    right:0;
-    border:0;
-}
 
 .preview {
     position: relative;
@@ -64,15 +51,18 @@
 .entry.show-presentation .preview,
 .entry.show-editor .editor,
 .entry.show-both .preview,
-.entry.show-both .editor {
+.entry.show-both .editor,
+.entry.show-warnings .editor,
+.entry.show-warnings .errors-el {
   opacity: 1;
   position: relative;
   pointer-events: all;
 }
 
 .show-editor       > .tabs > .editor-button,
 .show-presentation > .tabs > .pres-button,
-.show-both         > .tabs > .both-button {
+.show-both         > .tabs > .both-button,
+.show-warnings     > .tabs > .warnings-button {
     background: aliceblue;
 }
 .running-example.fullscreen {

diff --git a/docs/doc-repl/main.ml b/docs/doc-repl/main.ml
@@ -1,6 +1,6 @@
 open Code_mirror
 
-let view ~dimension ~preview_el ~editor_el starting =
+let view ~dimension ~preview_el ~errors_el ~editor_el starting =
   let open Editor in
   let basic_setup = Jv.get Jv.global "__CM__basic_setup" |> Extension.of_jv in
   let dark_mode =
@@ -14,6 +14,7 @@ let view ~dimension ~preview_el ~editor_el starting =
   let frontmatter =
     (Resolved
        {
+         external_ids = [];
          toplevel_attributes = None;
          math_link = None;
          theme = None;
@@ -32,7 +33,8 @@ let view ~dimension ~preview_el ~editor_el starting =
           basic_setup;
           markdown_extension;
           dark_mode;
-          Slipshow_communication.slipshow_plugin ~frontmatter preview_el;
+          Slipshow_communication.slipshow_plugin ~frontmatter ~errors_el
+            preview_el;
         |]
       ()
   in
@@ -42,74 +44,83 @@ let view ~dimension ~preview_el ~editor_el starting =
 
 let ( !! ) = Jstr.v
 
-let do_ ~dimension ~editor_el ~preview_el starting =
-  let _view = view ~dimension ~preview_el ~editor_el starting in
+let do_ ~dimension ~editor_el ~preview_el ~errors_el starting =
+  let _view : Editor.View.t =
+    view ~dimension ~preview_el ~errors_el ~editor_el starting
+  in
   ()
 
 type mode = Show_editor | Show_presentation | Show_both
 
 let all_modes = [ Show_both; Show_editor; Show_presentation ]
 
+let handle_elem =
+ fun el () ->
+  let open Brr in
+  let dimension =
+    El.at !!"dimension" el |> Option.map Jstr.to_string |> fun x ->
+    Option.bind x (fun s ->
+        match Slipshow.Frontmatter.Dimension.of_string s with
+        | Ok x -> Some x
+        | Error _ -> None)
+  in
+  let ffbs_unsafe c = El.find_first_by_selector ~root:el !!c |> Option.get in
+  let content =
+    let source = ffbs_unsafe ".source" in
+    Jv.get (Brr.El.to_jv source) "textContent" |> Jv.to_string
+  in
+  let editor_el = ffbs_unsafe ".editor" in
+  let errors_el = ffbs_unsafe ".errors-el" in
+  let preview_el = ffbs_unsafe ".preview" in
+  let editor_button = ffbs_unsafe ".editor-button" in
+  let pres_button = ffbs_unsafe ".pres-button" in
+  let both_button = ffbs_unsafe ".both-button" in
+  let fullscreen_button = ffbs_unsafe ".fullscreen-button" in
+  let () =
+    let fullscreen = ref false in
+    Ev.(listen click)
+      (fun _ ->
+        fullscreen := not !fullscreen;
+        El.set_class !!"fullscreen" !fullscreen el)
+      (El.as_target fullscreen_button)
+    |> ignore
+  in
+  let new_el = ffbs_unsafe ".entry" in
+  (* See also the python file _ext/slipshowexample.py *)
+  let mode_to_string = function
+    | Show_editor -> Jstr.v "show-editor"
+    | Show_presentation -> Jstr.v "show-presentation"
+    | Show_both -> Jstr.v "show-both"
+  in
+  let () =
+    let set_class v =
+      let set v b = El.set_class (mode_to_string v) b new_el in
+      List.iter (fun m -> set m false) all_modes;
+      set v true
+    in
+    let listen v el =
+      Ev.(listen click) (fun _ -> set_class v) (El.as_target el) |> ignore
+    in
+    listen Show_editor editor_button;
+    listen Show_presentation pres_button;
+    listen Show_both both_button
+  in
+  do_ ~dimension ~preview_el ~editor_el ~errors_el content
+
 let () =
   let _ =
     Brr.Ev.listen Brr.Ev.load
       (fun _ ->
+        let () =
+          match Brr.El.find_first_by_selector !!".running-example" with
+          | None -> ()
+          | Some _ ->
+              Brr.El.append_children
+                (Brr.Document.body Brr.G.document)
+                [ Brr.El.style [ Brr.El.txt' Ansi.css ] ]
+        in
         let _ =
-          Brr.El.fold_find_by_selector
-            (fun el () ->
-              let open Brr in
-              let dimension =
-                El.at !!"dimension" el |> Option.map Jstr.to_string |> fun x ->
-                Option.bind x (fun s ->
-                    match Slipshow.Frontmatter.String_to.dimension s with
-                    | Ok x -> Some x
-                    | Error _ -> None)
-              in
-              let ffbs_unsafe c =
-                El.find_first_by_selector ~root:el !!c |> Option.get
-              in
-              let content =
-                let source = ffbs_unsafe ".source" in
-                Jv.get (Brr.El.to_jv source) "textContent" |> Jv.to_string
-              in
-              let editor_el = ffbs_unsafe ".editor" in
-              let preview_el = ffbs_unsafe ".preview" in
-              let editor_button = ffbs_unsafe ".editor-button" in
-              let pres_button = ffbs_unsafe ".pres-button" in
-              let both_button = ffbs_unsafe ".both-button" in
-              let fullscreen_button = ffbs_unsafe ".fullscreen-button" in
-              let () =
-                let fullscreen = ref false in
-                Ev.(listen click)
-                  (fun _ ->
-                    fullscreen := not !fullscreen;
-                    El.set_class !!"fullscreen" !fullscreen el)
-                  (El.as_target fullscreen_button)
-                |> ignore
-              in
-              let new_el = ffbs_unsafe ".entry" in
-              (* See also the python file _ext/slipshowexample.py *)
-              let mode_to_string = function
-                | Show_editor -> Jstr.v "show-editor"
-                | Show_presentation -> Jstr.v "show-presentation"
-                | Show_both -> Jstr.v "show-both"
-              in
-              let () =
-                let set_class v =
-                  let set v b = El.set_class (mode_to_string v) b new_el in
-                  List.iter (fun m -> set m false) all_modes;
-                  set v true
-                in
-                let listen v el =
-                  Ev.(listen click) (fun _ -> set_class v) (El.as_target el)
-                  |> ignore
-                in
-                listen Show_editor editor_button;
-                listen Show_presentation pres_button;
-                listen Show_both both_button
-              in
-              do_ ~dimension ~preview_el ~editor_el content)
-            !!".running-example" ()
+          Brr.El.fold_find_by_selector handle_elem !!".running-example" ()
         in
         ())
       (Brr.Window.as_target Brr.G.window)

diff --git a/docs/frontmatter.rst b/docs/frontmatter.rst
@@ -40,3 +40,8 @@ The current options for the frontmatter are:
   a theme, corresponding to the name of a file in `this list
   <https://github.com/highlightjs/highlight.js/tree/5697ae5187746c24732e62cd625f3f83004a44ce/src/styles>`_,
   stripped from its extension.
+
+- ``external-ids``, for telling the slipshow compiler which ``ids`` will be
+  present even if they do not seem to be present in the document. This is just
+  in order to silence some warnings. This is useful when including svgs or math
+  where some IDs are given.
diff --git a/docs/manim.rst b/docs/manim.rst
diff --git a/docs/math.rst b/docs/math.rst
@@ -73,10 +73,17 @@ respectively assign an identifier, and a class.
 
 This allows to easily make them target of actions. For instance, one can use the ``pause`` action with a target to reveal content bit by bit. The ``reveal`` action and ``unrevealed`` class are also useful.
 
+Remember to use the ``external-ids`` field of the frontmatter to tell the
+compiler not to warn you that it cannot find the given ids.
+
 .. slipshow-example::
    :visible: both
    :dimension: 4:3
 
+   ---
+   external-ids: pause1 pause2
+   ---
+
    # Some title to make it more realistic
 
    ```math

diff --git a/docs/tikz.rst b/docs/tikz.rst
@@ -105,6 +105,7 @@ dynamics with actions:
 
    ---
    toplevel-attributes: slip enter=~duration:0 unreveal="c c-edges"
+   external-ids: c c-edges
    ---
 
    ![](triangle.svg){style="width:75%"}
@@ -113,14 +114,16 @@ dynamics with actions:
 
    {reveal=c-edges}
 
-Here is the final result!
+The ``external-ids`` field of the frontmatter tells the compiler not to warn you
+that it cannot find the given ids.  Here is the final result!
 
 .. slipshow-example::
    :visible: presentation
    :dimension: 4:3
 
    ---
    toplevel-attributes: slip enter=~duration:0 unreveal="c c-edges"
+   external-ids: c c-edges
    ---
 
    <!-- inlining the svg for simplicity -->

diff --git a/dune-project b/dune-project
@@ -24,6 +24,7 @@
  (depends
   (ocaml (>= 4.14))
    dune
+  (grace (>= 0.3.0))
   (crunch :with-dev-setup)
   (lambdasoup :with-test)
   (cmdliner (>= 1.3.0))
@@ -45,6 +46,7 @@
    sexplib
    ppx_sexp_conv
    ppx_deriving_yojson
+  (ansi (>= 0.7.0))
   (odoc :with-doc)
   (ocamlformat
    (and :with-dev-setup (= 0.27.0))))

diff --git a/example/funocaml-2025/main.md b/example/funocaml-2025/main.md
@@ -15,7 +15,7 @@ dimension: 16:9
 > {slip #part1 style="width:49%; height:" speaker-note=initial-sn}
 > {include src="slipshow.md"}
 >
-> {pause clear=draw-links reveal=surrprise}
+> {pause reveal=surrprise}
 >
 > {slip #my-part2 style="width:49%"}
 > {include src="three-simple-steps.md"}

diff --git a/example/funocaml-2025/slipshow.md b/example/funocaml-2025/slipshow.md
@@ -599,7 +599,7 @@ Say: "Slipshow has support for videos"
 }
 </style>
 
-{#video-demo .addons .block external}
+{#video-demo .addons .block}
 > ![](c6.mp4){style=width:100% #videoelem}
 
 {play-media=videoelem}

diff --git a/slipshow.opam b/slipshow.opam
@@ -13,6 +13,7 @@ bug-reports: "https://github.com/panglesd/slipshow/issues"
 depends: [
   "ocaml" {>= "4.14"}
   "dune" {>= "3.6"}
+  "grace" {>= "0.3.0"}
   "crunch" {with-dev-setup}
   "lambdasoup" {with-test}
   "cmdliner" {>= "1.3.0"}
@@ -34,6 +35,7 @@ depends: [
   "sexplib"
   "ppx_sexp_conv"
   "ppx_deriving_yojson"
+  "ansi" {>= "0.7.0"}
   "odoc" {with-doc}
   "ocamlformat" {with-dev-setup & = "0.27.0"}
 ]