function getRequestHeader(extensionsList) {
  if (!defined(extensionsList) || extensionsList.length === 0) {
    return {
      Accept:
        "application/vnd.quantized-mesh,application/octet-stream;q=0.9,*/*;q=0.01",
    };
  }
  const extensions = extensionsList.join("-");
  return {
    Accept: `application/vnd.quantized-mesh;extensions=${extensions},application/octet-stream;q=0.9,*/*;q=0.01`,
  };
}
A json object contain metadata about the tile

@type {number}
@constant
@default 4