# `html-cem/no-deprecated`

Warn on custom elements and attributes marked `deprecated` in the Custom Elements Manifest.

## Why

A `deprecated` flag on an element or attribute is an explicit migration signal from the component author. Surfacing it in the linter prevents silent accumulation of legacy usage.

## Rule details

- If an element's CEM declaration has `deprecated: true | string`, every usage of that tag is reported.
- If an attribute's CEM entry has `deprecated: true | string`, every usage of that attribute on the element is reported.
- When `deprecated` is a string, the message includes it (e.g. `"use <my-button> instead"`).

Default severity in the `recommended` config is `warn`.

## Examples

CEM marks `<my-old-thing>` and the `legacy-flag` attribute as deprecated.

❌ Reported

```html
<my-old-thing></my-old-thing>
<my-button label="Hi" legacy-flag></my-button>
```

✅ Not reported

```html
<my-button label="Hi"></my-button>
```