Characters that can break out of an inline style background-image url

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<div id="test" style="background-image: url($[chr];width:100%">hello</div>

let myDiv = document.getElementById("test");
// getComputedStyle().width returns the *used* value in px once the element has
// been laid out, so width:100% and width:auto both read as the same number of
// pixels and nothing is ever detected. Read the parsed inline declaration
// instead: it proves the ; terminated the url() token, and needs no layout.
if (myDiv.style.width === '100%') {
log(String.fromCharCode($[i]))
  }