message: edit comments.
diff: -// prefix that server.ts uses to distiguish requets on pdf files from others.
  -// '.' is chosen because it is not converted by encodeURIComponent and others.
  +// prefix that server.ts uses to distiguish requests on pdf files from others.
  +// We use '.' because it is not converted by encodeURIComponent and other functions.
  // See https://stackoverflow.com/questions/695438/safe-characters-for-friendly-url
  // See https://tools.ietf.org/html/rfc3986#section-2.3
  @@ -7,7 +7,7 @@ export const pdfFilePrefix = 'pdf..'
  // We encode the path with base64url after calling encodeURIComponent.
  // The reason not using base64url directly is that we are not sure that
  -// encodeURIComponent, unescape and btoa trick is valid on node.js.
  +// encodeURIComponent, unescape, and btoa trick is valid on node.js.
  // See https://en.wikipedia.org/wiki/Base64#URL_applications
  // See https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/btoa#Unicode_strings
  export function encodePath(path: string) {
  