Handleize
From Shopify Wiki
handleize(input) or handle(input)
This filter returns the Handle form of the input string, in the same way that Shopify generates handles out of the titles of products, pages, and collections. Non-word characters are stripped out and you end up with a nice lowercase dashed string which is suitable for constructing URLs, HTML attribute values, or anything else that shouldn't have spaces or strange characters.
Both handleize(input) and handle(input) return the same values.
Example:
<code>
<span class="variant {{ variant.title | handleize }}">{{ variant.title }}</span>
</code>