# Form Section Pattern

## Objective

Break long forms into labelled sections people can scan instead of read.

A section pattern grouping related fields under a heading, a description, and its own actions.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Find the forms that have grown past a screenful — settings, profiles, checkout, configuration — and group their fields by the question each group answers, not by the table the columns come from.
2. Give each section a heading in the document's heading order and an optional one-line description, so screen reader and keyboard users can jump between sections.
3. Allow at most one level of nesting. A section inside a section inside a tab gives the user no orientation and pushes the fields into a narrow gutter.
4. When validation fails, expand or scroll to the first section holding an error and mark every other affected section, so nothing stays hidden inside a collapsed group.
5. Do not treat sections as a substitute for splitting a genuinely multi-stage process. If the steps are sequential and have their own save points, that is a job for Stepper Component; sections group fields on one page.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Nesting sections more than one level deep destroys the scannability the pattern exists for — flatten, or split into separate pages.
- A collapsed section containing an invalid field must open on submit; leaving a hidden error with only a generic form-level failure message strands the user with no way to find it.
- Section-level actions such as add another or reset must stay reachable when the section is long, and must not be confused with the form's primary submit.
- On narrow screens the section heading, description, and fields need reduced vertical rhythm rather than the desktop spacing, or the form becomes an endless scroll.
- A section whose fields are all hidden by conditional logic must disappear entirely rather than leaving a heading with nothing under it.
- Collapsed state must not unmount the fields, or their values and validation state will be lost when the user opens the section again.
- Sections must not each own a save button while the form also has one — decide whether saving is per section or per form and apply it consistently.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Long forms are grouped into sections with headings in correct document order.
- [ ] Nesting never exceeds one level.
- [ ] Submitting an invalid form reveals every section containing an error.
- [ ] Collapsing a section preserves its field values and validation state.
- [ ] Sections with no visible fields are removed rather than left empty.
- [ ] Spacing adapts on narrow viewports without changing the grouping.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.