docs: add Formisch to form libraries section of forms guide

packages/dev/s2-docs/pages/react-aria/forms.mdx

@@ -443,7 +443,7 @@ export async function action({request}: Route.ActionArgs) {
 
 ## Form libraries
 
-In most cases, uncontrolled forms with the builtin validation features are sufficient. However, if you are building a truly complex form, or integrating React Aria components into an existing form, a separate form library such as [React Hook Form](https://react-hook-form.com/) or [Formik](https://formik.org/) may be helpful.
+In most cases, uncontrolled forms with the builtin validation features are sufficient. However, if you are building a truly complex form, or integrating React Aria components into an existing form, a separate form library such as [React Hook Form](https://react-hook-form.com/), [Formik](https://formik.org/), or [Formisch](https://formisch.dev/) may be helpful.
 
 ### React Hook Form
 
@@ -496,3 +496,51 @@ function App() {
 }
 ```
 
+### Formisch
+
+[Formisch](https://formisch.dev/) is a schema-based, headless form library for React. It validates with a [Valibot](https://valibot.dev/) schema and infers all input and output types directly from it.
+
+Use the `Field` component from Formisch to integrate React Aria components. The render prop provides the current value, error messages, and props for the field. Instead of spreading `field.props`, pass them individually: the ref goes to `inputRef` so Formisch registers the native input element, and `field.onChange` replaces the native change handler because React Aria passes the value instead of the event. The `Form` component from Formisch wraps a native `<form>` element and calls `onSubmit` with the validated values.
+
+```tsx
+import {Field, Form, useForm} from '@formisch/react';
+import * as v from 'valibot';
+import {TextField} from 'vanilla-starter/TextField';
+import {Button} from 'vanilla-starter/Button';
+
+const FormSchema = v.object({
+  name: v.pipe(v.string(), v.nonEmpty('Name is required.'))
+});
+
+function App() {
+  let form = useForm({schema: FormSchema});
+  let onSubmit = (output) => {
+    // Call your API here...
+  };
+
+  return (
+    <Form of={form} onSubmit={onSubmit}>
+      <Field of={form} path={['name']}>
+        {(field) => (
+          <TextField
+            label="Name"
+            name={field.props.name}
+            inputRef={field.props.ref}
+            value={field.input}
+            // React Aria passes the value instead of the event.
+            onChange={field.onChange}
+            onFocus={field.props.onFocus}
+            onBlur={field.props.onBlur}
+            isRequired
+            // Let Formisch handle validation instead of the browser.
+            validationBehavior="aria"
+            isInvalid={field.errors !== null}
+            errorMessage={field.errors?.[0]} />
+        )}
+      </Field>
+      <Button type="submit">Submit</Button>
+    </Form>
+  );
+}
+```
+