# The “gcse:search” element is a completely-unknown element that is not allowed anywhere in any HTML content.

> Canonical HTML version: https://rocketvalidator.com/html-validation/the-gcse-search-element-is-a-completely-unknown-element-that-is-not-allowed-anywhere-in-any-html-content
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

The `<gcse:search>` element is a custom tag from Google's Programmable Search Engine widget and is not part of any HTML specification.

Google's Programmable Search Engine (formerly Custom Search Engine) offers two ways to drop a search box onto a page. The older one uses namespaced tags such as `<gcse:search>`, `<gcse:searchbox>`, and `<gcse:searchresults>`, which the loaded `cse.js` script finds and replaces with the real widget. Browsers do not recognize the `gcse:` prefix, so they treat the tag as an unknown element, and the W3C validator rejects it because no such element exists in HTML.

Google supports an equivalent form that is valid HTML: a standard `<div>` carrying a `gcse-` class, like `<div class="gcse-search">`. The script reads the class instead of a custom tag name and renders the same search box. Switching to the class form clears the validation error without changing how the widget works.

## HTML examples

### Invalid: namespaced `<gcse:search>` element

```html
<script async src="https://cse.google.com/cse.js?cx=YOUR_SEARCH_ENGINE_ID"></script>
<gcse:search></gcse:search>
```

### Valid: div with the `gcse-search` class

```html
<script async src="https://cse.google.com/cse.js?cx=YOUR_SEARCH_ENGINE_ID"></script>
<div class="gcse-search"></div>
```

The same applies to the other Programmable Search tags: replace `<gcse:searchbox>` with `<div class="gcse-searchbox"></div>` and `<gcse:searchresults>` with `<div class="gcse-searchresults"></div>`. Each `gcse:` element has a matching `gcse-` class that produces the same result and passes validation.