# Copilot Instructions

## Core Requirements

- Follow project ESLINT configurations
- Ensure WCAG 2.2 Level AA compliance
- Apply Shift-Left security practices
- Adherence to Best Practices: All suggestions, architectural patterns, and solutions must align with widely accepted industry best practices and established design principles. Avoid experimental, obscure, or overly "creative" approaches. Stick to what is proven and reliable.
- Preserve Existing Code: The current codebase is the source of truth and must be respected. Prefer preservation of existing structure, style, and logic, however, present good alternatives where they exist.

## Code Style

### JavaScript/TypeScript

- None of my code is written in TypeScript, but I do use JSDoc comments and sometimes use .d.ts files to provide type information and help with editor intellisense
- For node.js, use features available to the latest LTS version but warn if using features not available to v18
- For browsers, use features available to 90%+ browsers/users
- No trailing semicolons
- Single quotes for strings
- Use trailing commas
- Indent code blocks with 4 spaces
- Use const by default, let when needed
- Prefer arrow functions
- Use optional chaining
- Add JSDoc if missing
- Add TypeScript types/interfaces
- Assume the use of ESLINT v9
- Prefer async/await over .then() syntax
- Prefer native CSS over JavaScript styling where possible

### Documentation

- Include JSDoc for functions and classes
- Place the first line of JSDoc description on the same line as the /**
- Add @param and @returns tags
- Document thrown errors
- Include usage examples for complex functions

### HTML/CSS

- Use semantic HTML elements
- Only use features available to 90%+ browsers/users
- Include ARIA attributes where needed
- Mobile-first responsive design
- Prefer relative sizing such as %, em or rem units
- Avoid the use of px sizing whenever possible
- Use CSS custom properties
- Follow BEM naming convention
- Include print styles
- Always use hsl colors
- Indent code blocks with 4 spaces
- Prefer native CSS over JavaScript styling where possible

## Testing

- Write unit tests using Vitest
- Include accessibility tests
- Maintain >80% code coverage
- Test error scenarios

## Performance

- Lazy load components when possible
- Optimize images and assets
- Keep bundle size minimal
- Use proper caching strategies

## Security

- Sanitize user inputs
- Validate data on server-side
- Follow OWASP guidelines
- Use Content Security Policy