function getClosestAttributeValue(elt, attributeName) {
    let closestAttr = null
    getClosestMatch(elt, function(e) {
      return !!(closestAttr = getAttributeValueWithDisinheritance(elt, asElement(e), attributeName))
    })
    if (closestAttr !== 'unset') {
      return closestAttr
    }
  }
@param {Element} elt
@param {string} attributeName
@returns {string | null}