我想知道这是什么意思？
usr/local/texlive/2019/texmf-dist/tex/latex/hyperref/hyperref.sty
Package hyperref Warning: Option `letterpaper' is no longer used.
这是我的作品：
\hypersetup{
plainpages=false, % needed if Roman numbers in frontpages
pdfpagelabels=true, % adds page number as label in Acrobat's page count
bookmarks=true, % show bookmarks bar?
unicode=false, % non-Latin characters in Acrobat's bookmarks
pdftoolbar=true, % show Acrobat's toolbar?
pdfmenubar=true, % show Acrobat's menu?
pdffitwindow=false, % window fit to page when opened
pdfstartview={FitH}, % fits the width of the page to the window
% pdftitle={uOttawa\ LaTeX\ Thesis\ Template}, % title: CHANGE THIS TEXT!
% pdfauthor={Author}, % author: CHANGE THIS TEXT! and uncomment this line
% pdfsubject={Subject}, % subject: CHANGE THIS TEXT! and uncomment this line
% pdfkeywords={keyword1} {key2} {key3}, % list of keywords, and uncomment this line if desired
pdfnewwindow=true, % links in new window
colorlinks=true, % false: boxed links; true: colored links
linkcolor=blue, % color of internal links
citecolor=green, % color of links to bibliography
filecolor=magenta, % color of file links
urlcolor=cyan % color of external links
\ifthenelse{\boolean{PrintVersion}}{ % for improved print quality, change some hyperref options
\hypersetup{ % override some previously defined hyperref options
% colorlinks,%
citecolor=black,%
filecolor=black,%
linkcolor=black,%
urlcolor=black}
}{} % end of ifthenelse (no else)
\documentclass[letterpaper,12pt,titlepage,oneside,final]{book}