hyperref-href-expansion.tex

\href{URL}{link text}

\DeclareRobustCommand*{\href}[1][]{%
  \begingroup
  \setkeys{href}{#1}%
  \@ifnextchar\bgroup\Hy@href{\hyper@normalise\href@}%
}

\begingroup
\Hy@href{github.com}{GitHub}

\def\Hy@href#{%
  \hyper@normalise\href@
}

\begingroup\begingroup
\hyper@normalise\href@{github.com}{GitHub}

\begingroup
\href@{github.com}{GitHub}

\begingroup
  \catcode`\$=6 % parameter character
  \catcode`\#=12 % other
  \gdef\href@$1{\expandafter\href@split$1##\\}%
  \gdef\href@split$1#$2#$3\\$4{%
    \hyper@@link{$1}{$2}{$4}%
    \endgroup
  }%
\endgroup
$%

\begingroup
\expandafter \href@split github.com##\\{GitHub}

\begingroup
\hyper@@link{github.com}{}{GitHub}
\endgroup

\def\hyper@@link{\let\Hy@reserved@a\relax
  \@ifnextchar[{\hyper@link@}{\hyper@link@[link]}%
}

\begingroup
\hyper@link@[link]{github.com}{}{GitHub}
\endgroup

\def\hyper@link@[#1]#2#3#4{%
  \ltx@ifempty{#4}{% link text
    \Hy@Warning{Suppressing empty link}%
  }{%
    \begingroup
      \protected@edef\Hy@tempa{#2}%
      \edef\Hy@tempb{#3}%
      \ifx\Hy@tempa\ltx@empty
        \ifx\Hy@tempb\ltx@empty
          \Hy@Warning{Suppressing link with empty target}%
          \toks@{%
            \endgroup
            \ltx@secondoftwo
          }%
        \else
          \toks@{%
            \endgroup
            \hyper@link{#1}%
          }%
        \fi
      \else
        \toks@{%
          \endgroup
          \expandafter\hyper@readexternallink#2\\{#1}%
        }%
      \fi
      \Hy@safe@activesfalse
      \toks@\expandafter{%
        \the\expandafter\toks@
        \expandafter{\Hy@tempb}{#4}%
      }%
    \the\toks@
  }%
}

\begingroup
\begingroup
\Hy@safe@activesfalse
\endgroup
\hyper@readexternallink github.com\\{link}{}{GitHub}
\endgroup


\def\hyper@readexternallink#1\\#2#3#4{%
  \begingroup
    \let\\\relax
  \expandafter\endgroup
  \expandafter\@@hyper@@readexternallink#1\\{#2}{#3}{#4}%
}

\begingroup
\@@hyper@@readexternallink github.com\\{link}{}{GitHub}
\endgroup

% URL or file name, type, internal name, link string
\def\@@hyper@@readexternallink#1\\#2#3#4{%
  \@hyper@readexternallink{#2}{#3}{#4}#1::\\{#1}%
}

\begingroup
\@hyper@readexternallink {link}{}{GitHub}https://github.com::\\{https://github.com}
\endgroup

% link type, internal name, link string
% URL type (http, mailto, file, ...), URL details, after ":"
% whole URL
\def\@hyper@readexternallink#1#2#3#4:#5:#6\\#7{%
  \ifx\\#6\\% local file
    \@hyper@linkfile file:#7\\{#3}{#2}{#7}%
  \else
    \ifx\\#4\\% mac filename
      \@hyper@linkfile file:#7\\{#3}{#2}{#7}%
    \else
      \def\@pdftempa{#4}%
      \ifx\@pdftempa\@pdftempwordfile
        \@hyper@linkfile#7\\{#3}{#2}{#7}%
      \else
        \ifx\@pdftempa\@pdftempwordrun
          \ifHy@pdfa
            \Hy@Error{%
              PDF/A: Launch action is prohibited%
            }\@ehc
            \begingroup
              \leavevmode
              #2%
            \endgroup
          \else
            \@hyper@launch#7\\{#3}{#2}%
          \fi
        \else
          \hyper@linkurl{#3}{#7\ifx\\#2\\\else\hyper@hash#2\fi}%
        \fi
      \fi
    \fi
  \fi
}

\begingroup
\@hyper@readexternallink {link}{}{GitHub}https://github.com::\\{https://github.com}

#1 {link}
#2 {}
#3 {GitHub}
#4 https
#5 //github.com
#6 :
#7 https://github.com

\hyper@linkurl{GitHub}{https://github.com}

\@hyper@readexternallink {link}{}{GitHub}github.tex::\\{github.tex}

#1 {link}
#2 {}
#3 {GitHub}
#4 github.tex
#5 
#6 
#7 github.tex

\@hyper@linkfile file:github.tex\\{GitHub}{}{github.tex}
\endgroup

\begingroup
% driver dependent
\hyper@linkurl{GitHub}{https://github.com}
\endgroup

% hpdftex.def
\def\hyper@linkurl#1#2{%
  \begingroup
    \Hy@pstringdef\Hy@pstringURI{#2}%
    \hyper@chars
    \leavevmode
    \pdfstartlink
      attr{%
        \Hy@setpdfborder
        \Hy@setpdfhighlight
        \ifx\@urlbordercolor\relax
        \else
          /C[\@urlbordercolor]%
        \fi
      }%
      user{%
       /Subtype/Link%
       \ifHy@pdfa /F 4\fi
       /A<<%
         /Type/Action%
         /S/URI%
         /URI(\Hy@pstringURI)%
         \ifHy@href@ismap
           /IsMap true%
         \fi
         \Hy@href@nextactionraw
       >>%
      }%
      \relax
    \Hy@colorlink\@urlcolor#1\Hy@xspace@end
    \close@pdflink
  \endgroup
}

\Hy@AtBeginDocument{%
  \def\Hy@colorlink#1{%
    \begingroup
      \ifHy@ocgcolorlinks
        \def\Hy@ocgcolor{#1}%
        \setbox0=\hbox\bgroup\color@begingroup
      \else
        \HyColor@UseColor#1%
      \fi
  }%
  \def\Hy@endcolorlink{%
    \ifHy@ocgcolorlinks
      \color@endgroup\egroup
      \mbox{%
        \pdfliteral page{/OC/OCPrint BDC}%
        \rlap{\copy0}%
        \pdfliteral page{EMC/OC/OCView BDC}%
        \begingroup
          \expandafter\HyColor@UseColor\Hy@ocgcolor
          \box0 %
        \endgroup
        \pdfliteral page{EMC}%
      }%
    \fi
    \endgroup
  }%
}%

\def\close@pdflink{%
  \Hy@endcolorlink
  \Hy@VerboseLinkStop
  \pdfendlink
}