function combineExtensions(extensions) {
  /** @type {NormalizedExtension} */
  const all = {}
  let index = -1

  while (++index < extensions.length) {
    syntaxExtension(all, extensions[index])
  }

  return all
}
Combine multiple syntax extensions into one.

@param {ReadonlyArray<Extension>} extensions
  List of syntax extensions.
@returns {NormalizedExtension}
  A single combined extension.