diff --git a/src/3x5.ts b/src/3x5.ts
index 620aa63..7ec7790 100644
--- a/src/3x5.ts
+++ b/src/3x5.ts
@@ -1,4 +1,4 @@
-import { Button } from './lib/button';
+import { Button, RegisterButtonOnClick } from './lib/button';
 import { Card, CardVm, GetField } from './lib/card';
 import { Here, RegisterJumpHere } from './lib/debug';
 import { Expr } from './lib/expr';
@@ -30,21 +30,6 @@ function parseFields(card: Card, fields: string) {
   }
 }
 
-/**
- * @param state VM state
- * @param code Script to run
- * @returns Markup to render / output
- */
-function renderCard(state: CardVm, code: string) {
-  const script = parse(code);
-  if (script[0]) {
-    runNoctl(state, script[1], (word) => (state.output += AsHtml(word) + "\n"));
-  } else {
-    state.output = script[1];
-  }
-  return state.output;
-}
-
 /**
  * Global state: a single card
  */
@@ -69,6 +54,12 @@ const codeInput = document.createElement("textarea");
 Object.assign(codeInput.style, TEXTAREA_STYLE, { height: "20em" });
 codeInput.value = String.raw`
 h1 [get title]
+
+button disabled
+button "Hello" -onClick {
+    alert Hiya
+}
+
 para [2 + 2]
 block {
     This is a paragraph of text, with one [b bold] word. Yes, this means there has to be some magic in text processing... <b>this</b> won't work.
@@ -116,29 +107,65 @@ const state = document.createElement("pre");
 const display = document.createElement("blockquote");
 const debugDisplay = document.createElement("pre");
 
+const COMMANDS = {
+  ...HTML,
+  get: GetField,
+  expr: Expr,
+  here: Here,
+  button: Button,
+};
+
 function render() {
   parseFields(theCard, fieldInput.value);
   theCard.code = codeInput.value;
 
   const vm: CardVm = {
-    mode: "render",
-    commands: {
-      ...HTML,
-      get: GetField,
-      expr: Expr,
-      here: Here,
-      button: Button,
-    },
+    mode: ["render"],
+    commands: COMMANDS,
     output: "",
     card: theCard,
   };
-  const html = renderCard(vm, theCard.code);
+
+  const script = parse(theCard.code);
+
+  let html = "";
+  if (script[0]) {
+    runNoctl(vm, script[1], (word) => (vm.output += AsHtml(word) + "\n"));
+  } else {
+    vm.output = script[1];
+  }
+  html = vm.output;
 
   state.textContent = JSON.stringify(theCard, null, 2);
   display.innerHTML = html;
   debugDisplay.textContent = html;
 }
 
+function triggerEvent(handlerPos: number) {
+  parseFields(theCard, fieldInput.value);
+  theCard.code = codeInput.value;
+
+  const vm: CardVm = {
+    mode: ["findingAction", handlerPos],
+    commands: COMMANDS,
+    output: "",
+    card: theCard,
+  };
+
+  const script = parse(theCard.code);
+
+  let html = "";
+  if (script[0]) {
+    runNoctl(vm, script[1], (word) => {});
+  } else {
+    vm.output = script[1];
+  }
+  html = vm.output;
+  console.debug(html);
+
+  state.textContent = JSON.stringify(theCard, null, 2);
+}
+
 render();
 document.body.append(
   fieldInput,
@@ -150,3 +177,4 @@ document.body.append(
 );
 
 RegisterJumpHere(codeInput);
+RegisterButtonOnClick(triggerEvent);
diff --git a/src/lib/button.ts b/src/lib/button.ts
index 780f7de..a76db46 100644
--- a/src/lib/button.ts
+++ b/src/lib/button.ts
@@ -1,5 +1,5 @@
 import { Proc } from '../vm';
-import { AsHtml, ProcResult, TextPiece } from '../words';
+import { AsHtml, ProcResult, SourcePos, TextPiece } from '../words';
 import { CardContext } from './card';
 import { getOptRaw } from './options';
 
@@ -10,7 +10,7 @@ export const Button: Proc<CardContext> = (vm, argv: TextPiece[]): ProcResult =>
     ({ onClick: [onClick = null] }, [label]) => {
       let buttonTrigger = "disabled";
       if (onClick && "pos" in onClick && onClick.pos != undefined) {
-        buttonTrigger = `data-notcl-onClick="${onClick.pos}"`;
+        buttonTrigger = `data-notcl-button="${onClick.pos}"`;
       }
 
       return {
@@ -18,3 +18,21 @@ export const Button: Proc<CardContext> = (vm, argv: TextPiece[]): ProcResult =>
       };
     }
   );
+
+export function RegisterButtonOnClick(
+  triggerDispatch: (pos: SourcePos) => void
+) {
+  document.body.addEventListener(
+    "click",
+    (evt) => {
+      const dataNoctlButton = (evt.target as HTMLElement)?.getAttribute?.(
+        "data-notcl-button"
+      );
+      if (dataNoctlButton !== null) {
+        const handlerPos = Number(dataNoctlButton);
+        triggerDispatch(handlerPos);
+      }
+    },
+    { passive: true }
+  );
+}
diff --git a/src/vm.ts b/src/vm.ts
index 8b68325..5a463db 100644
--- a/src/vm.ts
+++ b/src/vm.ts
@@ -1,15 +1,17 @@
 import {
-    AsText, Concat, ErrorResult, InterpolatedPiece, ProcResult, Script, TextPiece, Word
+    AsText, Concat, ErrorResult, InterpolatedPiece, ProcResult, Script, SourcePos, TextPiece, Word
 } from './words';
 
 /**
  * "Mode" of the environment a script runs in; determines access to mutability features and such.
  *
+ * "findingAction": preparing a response to a UI action, which can involve recalculating variables, but has no side-effects itself.
+ *
  * "action": response to a UI action; allowed to modify card fields and access time and random numbers.
  *
  * "render": deterministic generation of display markup from card and workspace state; can only modify temporary variables.
  */
-export type ScriptType = "action" | "render";
+export type ScriptType = ["findingAction", SourcePos] | ["action"] | ["render"];
 
 export type Proc<Context> = (
   state: Vm<Context>,