Package check result: NOTE

Check: CRAN incoming feasibility, Result: NOTE
  Maintainer: ‘Hadley Wickham <hadley@posit.co>’
  
  Found the following (possibly) invalid URLs:
    URL: https://www.amazon.com/Mastering-Regular-Expressions-Jeffrey-Friedl/dp/0596528124
      From: inst/doc/regular-expressions.html
      Status: 500
      Message: Internal Server Error

No changes to worse in reverse depends.