Function conditionalHeader

docs/tests/v2/es6/js/sanddance.js:153833–153843

(condition, element, header)

}

function conditionalHeader(condition, element, header) {
  var existing = existingHeader(element, header);

  if (condition && !existing) {
    addHeader(element, header);
  }

  if (!condition && existing) {
    existing.remove();
  }
}

function addHeader(element, header) {
  const h = document.createElement('h4');