diff --git a/app/editor/extensions/BlockMenu.tsx b/app/editor/extensions/BlockMenu.tsx
index a1551ad19f..59f3561c5d 100644
--- a/app/editor/extensions/BlockMenu.tsx
+++ b/app/editor/extensions/BlockMenu.tsx
@@ -6,10 +6,20 @@ import ReactDOM from "react-dom";
 import type { WidgetProps } from "@shared/editor/lib/Extension";
 import { PlaceholderPlugin } from "@shared/editor/plugins/PlaceholderPlugin";
 import { findParentNode } from "@shared/editor/queries/findParentNode";
+import type { Dictionary } from "~/hooks/useDictionary";
+import type { SuggestionOptions } from "~/editor/extensions/Suggestion";
 import Suggestion from "~/editor/extensions/Suggestion";
 import BlockMenu from "../components/BlockMenu";
 
-export default class BlockMenuExtension extends Suggestion {
+/**
+ * Options for the BlockMenu extension.
+ */
+type BlockMenuOptions = SuggestionOptions & {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+};
+
+export default class BlockMenuExtension extends Suggestion<BlockMenuOptions> {
   get defaultOptions() {
     return {
       trigger: "/",
diff --git a/app/editor/extensions/FindAndReplace.tsx b/app/editor/extensions/FindAndReplace.tsx
index d7be21a71c..db12f404ab 100644
--- a/app/editor/extensions/FindAndReplace.tsx
+++ b/app/editor/extensions/FindAndReplace.tsx
@@ -18,12 +18,22 @@ const pluginKey = new PluginKey("find-and-replace");
 const supportsHighlightAPI =
   typeof CSS !== "undefined" && CSS.highlights !== undefined;
 
-export default class FindAndReplaceExtension extends Extension {
+/**
+ * Options for the FindAndReplace extension.
+ */
+type FindAndReplaceOptions = {
+  /** Whether the search should be case sensitive by default. */
+  caseSensitive: boolean;
+  /** Whether the search query should be interpreted as a regular expression by default. */
+  regexEnabled: boolean;
+};
+
+export default class FindAndReplaceExtension extends Extension<FindAndReplaceOptions> {
   public get name() {
     return "find-and-replace";
   }
 
-  public get defaultOptions() {
+  public get defaultOptions(): FindAndReplaceOptions {
     return {
       caseSensitive: false,
       regexEnabled: false,
diff --git a/app/editor/extensions/HoverPreviews.tsx b/app/editor/extensions/HoverPreviews.tsx
index a485ea067a..d3ecb101b9 100644
--- a/app/editor/extensions/HoverPreviews.tsx
+++ b/app/editor/extensions/HoverPreviews.tsx
@@ -7,12 +7,15 @@ import stores from "~/stores";
 import HoverPreview from "~/components/HoverPreview";
 import env from "~/env";
 
+/**
+ * Options for the HoverPreviews extension.
+ */
 interface HoverPreviewsOptions {
-  /** Delay before the target is considered "hovered" and callback is triggered. */
+  /** Delay in milliseconds before the target is considered "hovered" and the preview is shown. */
   delay: number;
 }
 
-export default class HoverPreviews extends Extension {
+export default class HoverPreviews extends Extension<HoverPreviewsOptions> {
   state: {
     activeLinkElement: HTMLElement | null;
     unfurlId: string | null;
diff --git a/app/editor/extensions/Multiplayer.ts b/app/editor/extensions/Multiplayer.ts
index 87c469b509..27e3b5718c 100644
--- a/app/editor/extensions/Multiplayer.ts
+++ b/app/editor/extensions/Multiplayer.ts
@@ -1,3 +1,4 @@
+import type { HocuspocusProvider } from "@hocuspocus/provider";
 import isEqual from "lodash/isEqual";
 import { Plugin } from "prosemirror-state";
 import {
@@ -20,7 +21,19 @@ type UserAwareness = {
   head: object;
 };
 
-export default class Multiplayer extends Extension {
+/**
+ * Options for the Multiplayer extension.
+ */
+type MultiplayerOptions = {
+  /** The local user, used for cursor presence and the persistent user/client mapping. */
+  user: { id: string; color: string };
+  /** The Hocuspocus provider used for awareness and document sync. */
+  provider: HocuspocusProvider;
+  /** The shared Yjs document this editor is bound to. */
+  document: Y.Doc;
+};
+
+export default class Multiplayer extends Extension<MultiplayerOptions> {
   get name() {
     return "multiplayer";
   }
diff --git a/app/editor/extensions/SmartText.ts b/app/editor/extensions/SmartText.ts
index 1b31b1ca97..29ab5c1505 100644
--- a/app/editor/extensions/SmartText.ts
+++ b/app/editor/extensions/SmartText.ts
@@ -1,5 +1,6 @@
 import Extension from "@shared/editor/lib/Extension";
 import { InputRule } from "@shared/editor/lib/InputRule";
+import type { UserPreferences } from "@shared/types";
 
 const rightArrow = new InputRule(/->$/, "→");
 // Note that the suppression of pipe here prevents conflict with table creation rule.
@@ -19,7 +20,15 @@ const closeDoubleQuote = new InputRule(/^(?!.*`)[\s\S]*(")$/, "”");
 const openSingleQuote = new InputRule(/(?:^|[\s{[(<'"\u2018\u201C])(')$/, "‘");
 const closeSingleQuote = new InputRule(/^(?!.*`)[\s\S]*(')$/, "’");
 
-export default class SmartText extends Extension {
+/**
+ * Options for the SmartText extension.
+ */
+type SmartTextOptions = {
+  /** Display preferences for the logged in user, if any. */
+  userPreferences?: UserPreferences | null;
+};
+
+export default class SmartText extends Extension<SmartTextOptions> {
   get name() {
     return "smart_text";
   }
diff --git a/app/editor/extensions/Suggestion.ts b/app/editor/extensions/Suggestion.ts
index 0bb8342e5f..6904568bb2 100644
--- a/app/editor/extensions/Suggestion.ts
+++ b/app/editor/extensions/Suggestion.ts
@@ -7,15 +7,25 @@ import Extension from "@shared/editor/lib/Extension";
 import { SuggestionsMenuPlugin } from "@shared/editor/plugins/SuggestionsMenuPlugin";
 import { isInCode } from "@shared/editor/queries/isInCode";
 
-type Options = {
+/**
+ * Options shared by all suggestion-style extensions (block menu, emoji menu,
+ * mention menu).
+ */
+export type SuggestionOptions = {
+  /** Whether the suggestion menu is allowed to open inside code blocks or inline code. */
   enabledInCode: boolean;
+  /** Character (or list of characters) that opens the suggestion menu. */
   trigger: string | string[];
+  /** Whether spaces are allowed inside the search term. */
   allowSpaces: boolean;
+  /** Whether the menu only opens once at least one character has been typed after the trigger. */
   requireSearchTerm: boolean;
 };
 
-export default class Suggestion extends Extension {
-  constructor(options: Options) {
+export default class Suggestion<
+  TOptions extends SuggestionOptions = SuggestionOptions,
+> extends Extension<TOptions> {
+  constructor(options: TOptions) {
     super(options);
 
     const triggers = Array.isArray(this.options.trigger)
diff --git a/app/editor/extensions/index.ts b/app/editor/extensions/index.ts
index 5a4b592376..0b87b7a105 100644
--- a/app/editor/extensions/index.ts
+++ b/app/editor/extensions/index.ts
@@ -1,6 +1,4 @@
-import type Extension from "@shared/editor/lib/Extension";
-import type Mark from "@shared/editor/marks/Mark";
-import type Node from "@shared/editor/nodes/Node";
+import type { AnyExtensionClass } from "@shared/editor/lib/types";
 import BlockMenuExtension from "~/editor/extensions/BlockMenu";
 import ClipboardTextSerializer from "~/editor/extensions/ClipboardTextSerializer";
 import DiagramsExtension from "@shared/editor/extensions/Diagrams";
@@ -14,7 +12,7 @@ import PreventTab from "~/editor/extensions/PreventTab";
 import SelectionToolbarExtension from "~/editor/extensions/SelectionToolbar";
 import SmartText from "~/editor/extensions/SmartText";
 
-type Nodes = (typeof Node | typeof Mark | typeof Extension)[];
+type Nodes = AnyExtensionClass[];
 
 export const withUIExtensions = (nodes: Nodes) => [
   ...nodes,
diff --git a/app/editor/index.tsx b/app/editor/index.tsx
index 40d212bf8d..abb547f3c9 100644
--- a/app/editor/index.tsx
+++ b/app/editor/index.tsx
@@ -29,13 +29,11 @@ import insertFiles from "@shared/editor/commands/insertFiles";
 import Styles from "@shared/editor/components/Styles";
 import type { EmbedDescriptor } from "@shared/editor/embeds";
 import type { CommandFactory, WidgetProps } from "@shared/editor/lib/Extension";
-import type Extension from "@shared/editor/lib/Extension";
+import type { AnyExtension, AnyExtensionClass } from "@shared/editor/lib/types";
 import ExtensionManager from "@shared/editor/lib/ExtensionManager";
 import type { MarkdownSerializer } from "@shared/editor/lib/markdown/serializer";
 import textBetween from "@shared/editor/lib/textBetween";
-import type Mark from "@shared/editor/marks/Mark";
 import { basicExtensions as extensions } from "@shared/editor/nodes";
-import type Node from "@shared/editor/nodes/Node";
 import type ReactNode from "@shared/editor/nodes/ReactNode";
 import type { ComponentProps } from "@shared/editor/types";
 import type {
@@ -75,7 +73,7 @@ export type Props = {
   /** Placeholder displayed when the editor is empty */
   placeholder: string;
   /** Extensions to load into the editor */
-  extensions?: (typeof Node | typeof Mark | typeof Extension | Extension)[];
+  extensions?: (AnyExtensionClass | AnyExtension)[];
   /** If the editor should be focused on mount */
   autoFocus?: boolean;
   /** The focused comment, if any */
diff --git a/shared/editor/commands/link.ts b/shared/editor/commands/link.ts
index 1306af71d4..14f4e58c6a 100644
--- a/shared/editor/commands/link.ts
+++ b/shared/editor/commands/link.ts
@@ -2,6 +2,7 @@ import { chainCommands, toggleMark } from "prosemirror-commands";
 import type { Attrs } from "prosemirror-model";
 import type { Command } from "prosemirror-state";
 import { NodeSelection, Selection, TextSelection } from "prosemirror-state";
+import type * as React from "react";
 import { getMarkRange } from "../queries/getMarkRange";
 import { toast } from "sonner";
 import { sanitizeUrl } from "@shared/utils/urls";
@@ -49,8 +50,16 @@ const addLinkNodeSelection =
 
 const openLinkTextSelection =
   (
-    onClickLink: (url: string, event: KeyboardEvent) => void,
-    dictionary: Record<string, string>
+    onClickLink:
+      | ((
+          url: string,
+          event?:
+            | KeyboardEvent
+            | MouseEvent
+            | React.MouseEvent<HTMLButtonElement>
+        ) => void)
+      | undefined,
+    dictionary: { openLinkError: string }
   ): Command =>
   (state) => {
     if (!(state.selection instanceof TextSelection)) {
@@ -72,8 +81,16 @@ const openLinkTextSelection =
 
 const openLinkNodeSelection =
   (
-    onClickLink: (url: string, event: KeyboardEvent) => void,
-    dictionary: Record<string, string>
+    onClickLink:
+      | ((
+          url: string,
+          event?:
+            | KeyboardEvent
+            | MouseEvent
+            | React.MouseEvent<HTMLButtonElement>
+        ) => void)
+      | undefined,
+    dictionary: { openLinkError: string }
   ): Command =>
   (state) => {
     if (!(state.selection instanceof NodeSelection)) {
@@ -238,8 +255,13 @@ export const addLink = (attrs: Attrs): Command =>
   chainCommands(addLinkTextSelection(attrs), addLinkNodeSelection(attrs));
 
 export const openLink = (
-  onClickLink: (url: string, event: KeyboardEvent) => void,
-  dictionary: Record<string, string>
+  onClickLink:
+    | ((
+        url: string,
+        event?: KeyboardEvent | MouseEvent | React.MouseEvent<HTMLButtonElement>
+      ) => void)
+    | undefined,
+  dictionary: { openLinkError: string }
 ): Command =>
   chainCommands(
     openLinkTextSelection(onClickLink, dictionary),
diff --git a/shared/editor/extensions/Diff.ts b/shared/editor/extensions/Diff.ts
index d4e84fc98b..b5469f365d 100644
--- a/shared/editor/extensions/Diff.ts
+++ b/shared/editor/extensions/Diff.ts
@@ -13,12 +13,34 @@ import { toggleFoldPluginKey } from "../nodes/ToggleBlock";
 
 const pluginKey = new PluginKey("diffs");
 
-export default class Diff extends Extension {
+/**
+ * Options for the Diff extension.
+ */
+type DiffOptions = {
+  /** The set of changes to render as decorations, or null to disable diff rendering. */
+  changes: readonly ExtendedChange[] | null;
+  /** CSS class applied to inline insertions. */
+  insertionClassName: string;
+  /** CSS class applied to inline deletions. */
+  deletionClassName: string;
+  /** CSS class applied to whole-node insertions. */
+  nodeInsertionClassName: string;
+  /** CSS class applied to whole-node deletions. */
+  nodeDeletionClassName: string;
+  /** CSS class applied to inline modifications. */
+  modificationClassName: string;
+  /** CSS class applied to whole-node modifications. */
+  nodeModificationClassName: string;
+  /** CSS class applied to the change currently focused via navigation. */
+  currentChangeClassName: string;
+};
+
+export default class Diff extends Extension<DiffOptions> {
   get name() {
     return "diff";
   }
 
-  get defaultOptions() {
+  get defaultOptions(): DiffOptions {
     return {
       changes: null,
       insertionClassName: EditorStyleHelper.diffInsertion,
@@ -60,7 +82,7 @@ export default class Diff extends Extension {
    * @returns the total count of all inserted, deleted, and modified items.
    */
   public getTotalChangesCount(): number {
-    const { changes } = this.options as { changes: ExtendedChange[] | null };
+    const { changes } = this.options;
     if (!changes) {
       return 0;
     }
diff --git a/shared/editor/extensions/MaxLength.ts b/shared/editor/extensions/MaxLength.ts
index 8ace4eb8af..1ae02ac9e4 100644
--- a/shared/editor/extensions/MaxLength.ts
+++ b/shared/editor/extensions/MaxLength.ts
@@ -2,7 +2,15 @@ import type { Transaction } from "prosemirror-state";
 import { Plugin } from "prosemirror-state";
 import Extension from "../lib/Extension";
 
-export default class MaxLength extends Extension {
+/**
+ * Options for the MaxLength extension.
+ */
+type MaxLengthOptions = {
+  /** Maximum allowed document size, in ProseMirror node size units. */
+  maxLength?: number;
+};
+
+export default class MaxLength extends Extension<MaxLengthOptions> {
   get name() {
     return "maxlength";
   }
diff --git a/shared/editor/extensions/TrailingNode.ts b/shared/editor/extensions/TrailingNode.ts
index 553a93c7f8..45d56ec58b 100644
--- a/shared/editor/extensions/TrailingNode.ts
+++ b/shared/editor/extensions/TrailingNode.ts
@@ -2,12 +2,22 @@ import type { NodeType } from "prosemirror-model";
 import { Plugin, PluginKey } from "prosemirror-state";
 import Extension from "../lib/Extension";
 
-export default class TrailingNode extends Extension {
+/**
+ * Options for the TrailingNode extension.
+ */
+type TrailingNodeOptions = {
+  /** Name of the node type to insert as the trailing node. */
+  node: string;
+  /** Node names after which a trailing node should not be inserted. */
+  notAfter: string[];
+};
+
+export default class TrailingNode extends Extension<TrailingNodeOptions> {
   get name() {
     return "trailing_node";
   }
 
-  get defaultOptions() {
+  get defaultOptions(): TrailingNodeOptions {
     return {
       node: "paragraph",
       notAfter: ["paragraph", "heading"],
diff --git a/shared/editor/lib/Extension.ts b/shared/editor/lib/Extension.ts
index db13071099..2639e2501b 100644
--- a/shared/editor/lib/Extension.ts
+++ b/shared/editor/lib/Extension.ts
@@ -12,17 +12,15 @@ export type WidgetProps = {
   selection?: Selection;
 };
 
-export default class Extension {
-  // oxlint-disable-next-line @typescript-eslint/no-explicit-any
-  options: any;
+export default class Extension<TOptions extends object = object> {
+  options: TOptions;
   editor: Editor;
 
-  // oxlint-disable-next-line @typescript-eslint/no-explicit-any
-  constructor(options: Record<string, any> = {}) {
+  constructor(options: Partial<TOptions> = {}) {
     this.options = {
       ...this.defaultOptions,
       ...options,
-    };
+    } as TOptions;
   }
 
   bindEditor(editor: Editor) {
@@ -45,7 +43,7 @@ export default class Extension {
     return [];
   }
 
-  get defaultOptions() {
+  get defaultOptions(): Partial<TOptions> {
     return {};
   }
 
diff --git a/shared/editor/lib/ExtensionManager.ts b/shared/editor/lib/ExtensionManager.ts
index 12150bfdae..a58bad09be 100644
--- a/shared/editor/lib/ExtensionManager.ts
+++ b/shared/editor/lib/ExtensionManager.ts
@@ -10,26 +10,22 @@ import type Mark from "../marks/Mark";
 import type Node from "../nodes/Node";
 import type { CommandFactory, WidgetProps } from "./Extension";
 import type Extension from "./Extension";
+import type { AnyExtension, AnyExtensionClass } from "./types";
 import makeRules from "./markdown/rules";
 import { MarkdownSerializer } from "./markdown/serializer";
 
 export default class ExtensionManager {
-  extensions: (Node | Mark | Extension)[] = [];
+  extensions: AnyExtension[] = [];
   readOnly: boolean;
 
   constructor(
-    extensions: (
-      | Extension
-      | typeof Node
-      | typeof Mark
-      | typeof Extension
-    )[] = [],
+    extensions: (AnyExtensionClass | AnyExtension)[] = [],
     editor?: Editor
   ) {
     this.readOnly = editor?.props.readOnly ?? false;
 
     extensions.forEach((ext) => {
-      let extension;
+      let extension: AnyExtension;
 
       if (typeof ext === "function") {
         // Check the prototype before instantiation to avoid constructor cost
@@ -42,8 +38,12 @@ export default class ExtensionManager {
           return;
         }
 
-        // @ts-expect-error We won't instantiate an abstract class
-        extension = new ext(editor?.props);
+        // Cast away abstract: registration treats all classes uniformly and
+        // concrete subclasses are required at the public boundary.
+        const Ctor = ext as new (
+          options?: Record<string, unknown>
+        ) => AnyExtension;
+        extension = new Ctor(editor?.props);
       } else {
         // For already-instantiated extensions, check the instance.
         if (this.readOnly && ext.type === "extension" && !ext.allowInReadOnly) {
@@ -205,35 +205,40 @@ export default class ExtensionManager {
   keymaps({ schema }: { schema: Schema }) {
     const keymaps = this.extensions
       .filter((extension) => extension.keys)
-      .map((extension) =>
-        ["node", "mark"].includes(extension.type)
-          ? extension.keys({
-              // @ts-expect-error TODO
-              type: schema[`${extension.type}s`][extension.name],
-              schema,
-            })
-          : (extension as Extension).keys({ schema })
-      );
+      .map((extension) => {
+        if (extension.type === "node") {
+          const node = extension as Node;
+          return node.keys({ type: schema.nodes[node.name], schema });
+        }
+        if (extension.type === "mark") {
+          const mark = extension as Mark;
+          return mark.keys({ type: schema.marks[mark.name], schema });
+        }
+        return (extension as Extension).keys({ schema });
+      });
 
     return keymaps.map(keymap);
   }
 
   inputRules({ schema }: { schema: Schema }) {
     const extensionInputRules = this.extensions
-      .filter((extension) => ["extension"].includes(extension.type))
+      .filter((extension) => extension.type === "extension")
       .filter((extension) => extension.inputRules)
       .map((extension: Extension) => extension.inputRules({ schema }));
 
     const nodeMarkInputRules = this.extensions
-      .filter((extension) => ["node", "mark"].includes(extension.type))
+      .filter(
+        (extension) => extension.type === "node" || extension.type === "mark"
+      )
       .filter((extension) => extension.inputRules)
-      .map((extension) =>
-        extension.inputRules({
-          // @ts-expect-error TODO
-          type: schema[`${extension.type}s`][extension.name],
-          schema,
-        })
-      );
+      .map((extension) => {
+        if (extension.type === "node") {
+          const node = extension as Node;
+          return node.inputRules({ type: schema.nodes[node.name], schema });
+        }
+        const mark = extension as Mark;
+        return mark.inputRules({ type: schema.marks[mark.name], schema });
+      });
 
     return [...extensionInputRules, ...nodeMarkInputRules].reduce(
       (allInputRules, inputRules) => [...allInputRules, ...inputRules],
@@ -245,19 +250,19 @@ export default class ExtensionManager {
     return this.extensions
       .filter((extension) => extension.commands)
       .reduce((allCommands, extension) => {
-        const { name, type } = extension;
+        const { name } = extension;
         const commands: Record<string, CommandFactory> = {};
 
-        // @ts-expect-error FIXME
-        const value = extension.commands({
-          schema,
-          ...(["node", "mark"].includes(type)
-            ? {
-                // @ts-expect-error TODO
-                type: schema[`${type}s`][name],
-              }
-            : {}),
-        });
+        let value: ReturnType<Extension["commands"]>;
+        if (extension.type === "node") {
+          const node = extension as Node;
+          value = node.commands({ schema, type: schema.nodes[node.name] });
+        } else if (extension.type === "mark") {
+          const mark = extension as Mark;
+          value = mark.commands({ schema, type: schema.marks[mark.name] });
+        } else {
+          value = (extension as Extension).commands({ schema });
+        }
 
         const apply = (
           callback: CommandFactory,
diff --git a/shared/editor/lib/types.ts b/shared/editor/lib/types.ts
new file mode 100644
index 0000000000..4853ae12c9
--- /dev/null
+++ b/shared/editor/lib/types.ts
@@ -0,0 +1,19 @@
+import type Mark from "../marks/Mark";
+import type Node from "../nodes/Node";
+import type Extension from "./Extension";
+
+/**
+ * Type-erased Extension, Mark, or Node instance. Used at registration
+ * boundaries where the specific options shape is not relevant.
+ */
+// oxlint-disable-next-line @typescript-eslint/no-explicit-any
+export type AnyExtension = Extension<any> | Mark<any> | Node<any>;
+
+/**
+ * Constructor for any Extension, Mark, or Node subclass, regardless of its
+ * options shape.
+ */
+export type AnyExtensionClass = abstract new (
+  // oxlint-disable-next-line @typescript-eslint/no-explicit-any
+  ...args: any[]
+) => AnyExtension;
diff --git a/shared/editor/marks/Comment.ts b/shared/editor/marks/Comment.ts
index e073bde68a..3492926fa6 100644
--- a/shared/editor/marks/Comment.ts
+++ b/shared/editor/marks/Comment.ts
@@ -10,7 +10,25 @@ import { isMarkActive } from "../queries/isMarkActive";
 import { EditorStyleHelper } from "../styles/EditorStyleHelper";
 import Mark from "./Mark";
 
-export default class Comment extends Mark {
+/**
+ * Options for the Comment mark.
+ */
+type CommentOptions = {
+  /** The id of the current user, recorded on newly created comment marks. */
+  userId?: string;
+  /** Callback invoked when a comment mark is created in the document. */
+  onCreateCommentMark?: (
+    commentId: string,
+    userId: string,
+    options?: { focus: boolean }
+  ) => void;
+  /** Callback invoked when an existing comment mark is clicked. */
+  onClickCommentMark?: (commentId: string) => void;
+  /** Callback invoked to request that the comments sidebar be opened. */
+  onOpenCommentsSidebar?: () => void;
+};
+
+export default class Comment extends Mark<CommentOptions> {
   get name() {
     return "comment";
   }
diff --git a/shared/editor/marks/Link.tsx b/shared/editor/marks/Link.tsx
index b474b30b98..dbe46099f1 100644
--- a/shared/editor/marks/Link.tsx
+++ b/shared/editor/marks/Link.tsx
@@ -12,6 +12,7 @@ import type { Command, EditorState } from "prosemirror-state";
 import { Plugin, TextSelection } from "prosemirror-state";
 import type { EditorView } from "prosemirror-view";
 import { toast } from "sonner";
+import type { Dictionary } from "~/hooks/useDictionary";
 import { isUrl, sanitizeUrl } from "../../utils/urls";
 import { getMarkRange } from "../queries/getMarkRange";
 import Mark from "./Mark";
@@ -53,7 +54,20 @@ function isPlainURL(
   return !link.isInSet(next.marks);
 }
 
-export default class Link extends Mark {
+/**
+ * Options for the Link mark.
+ */
+type LinkOptions = {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+  /** Callback invoked when the user clicks any link in the document. */
+  onClickLink?: (
+    href: string,
+    event?: MouseEvent | React.MouseEvent<HTMLButtonElement>
+  ) => void;
+};
+
+export default class Link extends Mark<LinkOptions> {
   get name() {
     return "link";
   }
@@ -208,10 +222,11 @@ export default class Link extends Mark {
                   : "");
 
               try {
-                if (this.options.onClickLink && href) {
+                const sanitized = sanitizeUrl(href);
+                if (this.options.onClickLink && sanitized) {
                   event.stopPropagation();
                   event.preventDefault();
-                  this.options.onClickLink(sanitizeUrl(href), event);
+                  this.options.onClickLink(sanitized, event);
                 }
               } catch (_err) {
                 toast.error(this.options.dictionary.openLinkError);
diff --git a/shared/editor/marks/Mark.ts b/shared/editor/marks/Mark.ts
index d89543f519..180a777743 100644
--- a/shared/editor/marks/Mark.ts
+++ b/shared/editor/marks/Mark.ts
@@ -13,7 +13,9 @@ import Extension from "../lib/Extension";
 import type { MarkdownSerializerState } from "../lib/markdown/serializer";
 import type { Primitive } from "utility-types";
 
-export default abstract class Mark extends Extension {
+export default abstract class Mark<
+  TOptions extends object = object,
+> extends Extension<TOptions> {
   get type() {
     return "mark";
   }
diff --git a/shared/editor/nodes/Attachment.tsx b/shared/editor/nodes/Attachment.tsx
index a1b0e416f1..ec7923397f 100644
--- a/shared/editor/nodes/Attachment.tsx
+++ b/shared/editor/nodes/Attachment.tsx
@@ -9,6 +9,7 @@ import type { Command } from "prosemirror-state";
 import { NodeSelection } from "prosemirror-state";
 import { Trans } from "react-i18next";
 import type { Primitive } from "utility-types";
+import type { Dictionary } from "~/hooks/useDictionary";
 import { bytesToHumanReadable, getEventFiles } from "../../utils/files";
 import { sanitizeUrl } from "../../utils/urls";
 import insertFiles from "../commands/insertFiles";
@@ -21,7 +22,15 @@ import type { ComponentProps } from "../types";
 import Node from "./Node";
 import PdfViewer from "../components/PDF";
 
-export default class Attachment extends Node {
+/**
+ * Options for the Attachment node.
+ */
+type AttachmentOptions = {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+};
+
+export default class Attachment extends Node<AttachmentOptions> {
   get name() {
     return "attachment";
   }
diff --git a/shared/editor/nodes/CodeFence.ts b/shared/editor/nodes/CodeFence.ts
index 23b9f7eadb..3cbd1df549 100644
--- a/shared/editor/nodes/CodeFence.ts
+++ b/shared/editor/nodes/CodeFence.ts
@@ -145,17 +145,21 @@ function buildCollapseState(
   };
 }
 
-export default class CodeFence extends Node {
+/**
+ * Options for the CodeFence node.
+ */
+type CodeFenceOptions = {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+  /** Display preferences for the logged in user, if any. */
+  userPreferences?: UserPreferences | null;
+};
+
+export default class CodeFence extends Node<CodeFenceOptions> {
   /** Plugin key for the collapse state, shared with the command. */
   private static readonly collapseKey = new PluginKey<CollapseState>(
     "collapse-code-block"
   );
-  constructor(options: {
-    dictionary: Dictionary;
-    userPreferences?: UserPreferences | null;
-  }) {
-    super(options);
-  }
 
   get showLineNumbers(): boolean {
     return this.options.userPreferences?.codeBlockLineNumbers ?? true;
diff --git a/shared/editor/nodes/Doc.ts b/shared/editor/nodes/Doc.ts
index c44811c0d9..7f6670e996 100644
--- a/shared/editor/nodes/Doc.ts
+++ b/shared/editor/nodes/Doc.ts
@@ -3,7 +3,15 @@ import type { NodeSpec } from "prosemirror-model";
 import { PlaceholderPlugin } from "../plugins/PlaceholderPlugin";
 import Node from "./Node";
 
-export default class Doc extends Node {
+/**
+ * Options for the Doc node.
+ */
+type DocOptions = {
+  /** Placeholder text shown when the document is empty. */
+  placeholder: string;
+};
+
+export default class Doc extends Node<DocOptions> {
   get name() {
     return "doc";
   }
diff --git a/shared/editor/nodes/Heading.ts b/shared/editor/nodes/Heading.ts
index 477522afca..55b0881bf6 100644
--- a/shared/editor/nodes/Heading.ts
+++ b/shared/editor/nodes/Heading.ts
@@ -13,6 +13,7 @@ import { Decoration, DecorationSet } from "prosemirror-view";
 import { toast } from "sonner";
 import type { Primitive } from "utility-types";
 import { isSafari } from "../../utils/browser";
+import type { Dictionary } from "~/hooks/useDictionary";
 import Storage from "../../utils/Storage";
 import backspaceToParagraph from "../commands/backspaceToParagraph";
 import splitHeading from "../commands/splitHeading";
@@ -30,15 +31,26 @@ export enum HeadingLevel {
   Four,
 }
 
-export default class Heading extends Node {
+/**
+ * Options for the Heading node.
+ */
+type HeadingOptions = {
+  /** Heading levels (1-based) that are enabled in this editor. */
+  levels: number[];
+  /** Offset added to the rendered heading level (e.g. 1 renders an `h2` for level 1). */
+  offset?: number;
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+};
+
+export default class Heading extends Node<HeadingOptions> {
   get name() {
     return "heading";
   }
 
-  get defaultOptions() {
+  get defaultOptions(): Partial<HeadingOptions> {
     return {
       levels: [1, 2, 3, 4],
-      collapsed: undefined,
     };
   }
 
diff --git a/shared/editor/nodes/Node.ts b/shared/editor/nodes/Node.ts
index 8e206857e9..862a3cd6c8 100644
--- a/shared/editor/nodes/Node.ts
+++ b/shared/editor/nodes/Node.ts
@@ -11,7 +11,9 @@ import type { CommandFactory } from "../lib/Extension";
 import Extension from "../lib/Extension";
 import type { MarkdownSerializerState } from "../lib/markdown/serializer";
 
-export default abstract class Node extends Extension {
+export default abstract class Node<
+  TOptions extends object = object,
+> extends Extension<TOptions> {
   get type() {
     return "node";
   }
diff --git a/shared/editor/nodes/ReactNode.ts b/shared/editor/nodes/ReactNode.ts
index f193cc293b..12f2730aa5 100644
--- a/shared/editor/nodes/ReactNode.ts
+++ b/shared/editor/nodes/ReactNode.ts
@@ -1,7 +1,9 @@
 import type { ComponentProps } from "../types";
 import Node from "./Node";
 
-export default abstract class ReactNode extends Node {
+export default abstract class ReactNode<
+  TOptions extends object = object,
+> extends Node<TOptions> {
   abstract component: (
     props: Omit<ComponentProps, "theme">
   ) => React.ReactElement;
diff --git a/shared/editor/nodes/ToggleBlock.ts b/shared/editor/nodes/ToggleBlock.ts
index a9b2c5117a..be59c398c6 100644
--- a/shared/editor/nodes/ToggleBlock.ts
+++ b/shared/editor/nodes/ToggleBlock.ts
@@ -12,6 +12,7 @@ import { Plugin, PluginKey, TextSelection } from "prosemirror-state";
 import { findWrapping } from "prosemirror-transform";
 import { Decoration, DecorationSet } from "prosemirror-view";
 import { v4 } from "uuid";
+import type { Dictionary } from "~/hooks/useDictionary";
 import Storage from "../../utils/Storage";
 import {
   deleteSelectionPreservingBody,
@@ -64,7 +65,15 @@ export const toggleEventPluginKey = new PluginKey("toggleBlockEvent");
 /** Build the localStorage key used to persist a toggle block's fold state. */
 export const toggleStorageKey = (id: string) => `toggle:${id}`;
 
-export default class ToggleBlock extends Node {
+/**
+ * Options for the ToggleBlock node.
+ */
+type ToggleBlockOptions = {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary?: Dictionary;
+};
+
+export default class ToggleBlock extends Node<ToggleBlockOptions> {
   get name() {
     return "container_toggle";
   }
@@ -340,7 +349,7 @@ export default class ToggleBlock extends Node {
             parent.type.name === "container_toggle" &&
             $start.index($start.depth - 1) === 0 &&
             node.textContent === "",
-          text: this.options.dictionary?.emptyToggleBlockHead,
+          text: this.options.dictionary?.emptyToggleBlockHead ?? "",
         },
         {
           condition: ({ parent, $start, state }) =>
@@ -350,7 +359,7 @@ export default class ToggleBlock extends Node {
             ToggleBlock.isBodyEmpty(parent) &&
             (state.selection.$from.pos < $start.pos ||
               state.selection.$from.pos > $start.end($start.depth - 1)),
-          text: this.options.dictionary?.emptyToggleBlockBody,
+          text: this.options.dictionary?.emptyToggleBlockBody ?? "",
         },
         {
           condition: ({ node, parent, $start, state }) =>
@@ -359,7 +368,7 @@ export default class ToggleBlock extends Node {
             node.isTextblock &&
             node.textContent === "" &&
             (state.selection as TextSelection).$cursor?.pos === $start.pos,
-          text: this.options.dictionary?.newLineEmpty,
+          text: this.options.dictionary?.newLineEmpty ?? "",
         },
       ]),
     ];
diff --git a/shared/editor/nodes/Video.tsx b/shared/editor/nodes/Video.tsx
index 4aaeb6f58a..f5e9179381 100644
--- a/shared/editor/nodes/Video.tsx
+++ b/shared/editor/nodes/Video.tsx
@@ -7,6 +7,7 @@ import type {
 import { NodeSelection, TextSelection } from "prosemirror-state";
 import * as React from "react";
 import type { Primitive } from "utility-types";
+import type { Dictionary } from "~/hooks/useDictionary";
 import { sanitizeUrl } from "../../utils/urls";
 import toggleWrap from "../commands/toggleWrap";
 import Caption from "../components/Caption";
@@ -16,7 +17,15 @@ import attachmentsRule from "../rules/links";
 import type { ComponentProps } from "../types";
 import Node from "./Node";
 
-export default class Video extends Node {
+/**
+ * Options for the Video node.
+ */
+type VideoOptions = {
+  /** A dictionary of translated strings used in the editor. */
+  dictionary: Dictionary;
+};
+
+export default class Video extends Node<VideoOptions> {
   get name() {
     return "video";
   }
diff --git a/shared/editor/nodes/index.ts b/shared/editor/nodes/index.ts
index 5192808349..ff3d3be55b 100644
--- a/shared/editor/nodes/index.ts
+++ b/shared/editor/nodes/index.ts
@@ -4,14 +4,13 @@ import HexColorPreview from "../extensions/HexColorPreview";
 import History from "../extensions/History";
 import MaxLength from "../extensions/MaxLength";
 import TrailingNode from "../extensions/TrailingNode";
-import type Extension from "../lib/Extension";
+import type { AnyExtensionClass } from "../lib/types";
 import Bold from "../marks/Bold";
 import Code from "../marks/Code";
 import Comment from "../marks/Comment";
 import Highlight from "../marks/Highlight";
 import Italic from "../marks/Italic";
 import Link from "../marks/Link";
-import type Mark from "../marks/Mark";
 import TemplatePlaceholder from "../marks/Placeholder";
 import Strikethrough from "../marks/Strikethrough";
 import Underline from "../marks/Underline";
@@ -33,7 +32,6 @@ import ListItem from "./ListItem";
 import Math from "./Math";
 import MathBlock from "./MathBlock";
 import Mention from "./Mention";
-import type Node from "./Node";
 import Notice from "./Notice";
 import OrderedList from "./OrderedList";
 import Paragraph from "./Paragraph";
@@ -47,7 +45,7 @@ import ToggleBlock from "./ToggleBlock";
 
 import Video from "./Video";
 
-type Nodes = (typeof Node | typeof Mark | typeof Extension)[];
+type Nodes = AnyExtensionClass[];
 
 /**
  * A set of inline nodes that are used in the editor. This is used for simple