JSFiddle - React, Tailwind, and code Playground

HTML

<a data-éxample href=http://stackoverflow.com/questions/13283699/sanitize-attribute-name>example - click to see related question</a>

CSS

/* this works with or w/o the slash, but does not validate in either case */
[data-\éxample] { 
    background: #8d2; padding: 4px;
    display:block; font-family: monospace; 
}

JavaScript

console.log( document.querySelectorAll("[data-éxample]") );