% \iffalse meta-comment
%
%% File: l3backend-pdfannot.dtx
%
% Copyright (C) 2025 The LaTeX Project
%
% It may be distributed and/or modified under the conditions of the
% LaTeX Project Public License (LPPL), either version 1.3c of this
% license or (at your option) any later version.  The latest version
% of this license is in the file
%
%    https://www.latex-project.org/lppl.txt
%
% This file is part of the "l3backend bundle" (The Work in LPPL)
% and all files in that bundle must be distributed together.
%
% -----------------------------------------------------------------------
%
% The development version of the bundle can be found at
%
%    https://github.com/latex3/latex3
%
% for those people who are interested.
%
%<*driver>
\documentclass[full,kernel]{l3doc}
\begin{document}
  \DocInput{\jobname.dtx}
\end{document}
%</driver>
% \fi
%
% \title{^^A
%   The \pkg{l3backend-pdfannot} module\\ Backend PDF annotation features^^A
% }
%
% \author{^^A
%  The \LaTeX{} Project\thanks
%    {^^A
%      E-mail:
%        \href{mailto:latex-team@latex-project.org}
%          {latex-team@latex-project.org}^^A
%    }^^A
% }
%
% \date{Released 2025-03-10}
%
% \maketitle
%
% \begin{documentation}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{\pkg{l3backend-pdfannot} implementation}
%
%    \begin{macrocode}
%<*package>
%<@@=pdfannot>
%    \end{macrocode}
%
% \subsection{\texttt{dvips} backend}
%
%    \begin{macrocode}
%<*dvips>
%    \end{macrocode}
%
% In \texttt{dvips}, annotations have to be constructed manually. As such,
% we need the object code above for some definitions.
%
% \begin{variable}{\l_@@_backend_content_box}
%   The content of an annotation.
%    \begin{macrocode}
\box_new:N \l_@@_backend_content_box
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_backend_model_box}
%   For creating model sizing for links.
%    \begin{macrocode}
\box_new:N \l_@@_backend_model_box
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\g_@@_backend_int}
%   Needed to track annotations.
%    \begin{macrocode}
\int_new:N \g_@@_backend_int
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}{\@@_backend_generic:nnnn, \@@_backend_generic_aux:nnnn}
%   Annotations are objects but they are not in the object data lists. Here, to
%   get the coordinates of the annotation, we need to have the data collected
%   at the PostScript level. That requires a bit of box trickery (effectively a
%   \LaTeXe{} |picture| of zero size). Once the data is collected, use it to
%   set up the annotation border.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_generic:nnnn #1#2#3#4
  {
    \exp_args:Nf \@@_backend_generic_aux:nnnn
      { \dim_eval:n {#1} } {#2} {#3} {#4}
  }
\cs_new_protected:Npn \@@_backend_generic_aux:nnnn #1#2#3#4
  {
    \box_move_down:nn {#3}
      { \hbox:n { \__kernel_backend_postscript:n { pdfannot.save.ll } } }
    \box_move_up:nn {#2}
      {
        \hbox:n
          {
            \__kernel_kern:n {#1}
            \__kernel_backend_postscript:n { pdfannot.save.ur }
            \__kernel_kern:n { -#1 }
          }
      }
    \int_gincr:N \g_@@_backend_int
    \__kernel_backend_postscript:e
      {
        mark
        /_objdef { pdfannot \int_use:N \g_@@_backend_int }
        pdfannot.rect
        #4 ~
        /ANN ~
        pdfmark
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_backend_last:}
%   Provide the last annotation we created: could get tricky of course if
%   other packages are loaded.
%    \begin{macrocode}
\cs_new:Npn \@@_backend_last:
  { { pdfannot \int_use:N \g_@@_backend_int } }
%    \end{macrocode}
% \end{macro}
%
% \begin{variable}{\g_@@_backend_link_int}
%   To track annotations which are links.
%    \begin{macrocode}
\int_new:N \g_@@_backend_link_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\g_@@_backend_link_dict_tl}
%   To pass information to the end-of-link function.
%    \begin{macrocode}
\tl_new:N \g_@@_backend_link_dict_tl
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\g_@@_backend_link_sf_int}
%   Needed to save/restore space factor, which is needed to deal with the face
%   we need a box.
%    \begin{macrocode}
\int_new:N \g_@@_backend_link_sf_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\g_@@_backend_link_math_bool}
%   Needed to save/restore math mode.
%    \begin{macrocode}
\bool_new:N \g_@@_backend_link_math_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\g_@@_backend_link_bool}
%   Track link formation: we cannot nest at all.
%    \begin{macrocode}
\bool_new:N \g_@@_backend_link_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_backend_breaklink_pdfmark_tl}
%   Swappable content for link breaking.
%    \begin{macrocode}
\tl_new:N \l_@@_backend_breaklink_pdfmark_tl
\tl_set:Nn \l_@@_backend_breaklink_pdfmark_tl { pdfmark }
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}{\@@_backend_breaklink_postscript:n}
%   To allow dropping material unless link breaking is active.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_breaklink_postscript:n #1 { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_breaklink_usebox:N}
%   Swappable box unpacking or use.
%    \begin{macrocode}
\cs_new_eq:NN \@@_backend_breaklink_usebox:N \box_use:N
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}
%   {\@@_backend_link_begin_goto:nnw, \@@_backend_link_begin_user:nnw}
% \begin{macro}{\@@_backend_link:nw, \@@_backend_link_aux:nw}
% \begin{macro}{\@@_backend_link_end:, \@@_backend_link_end_aux:}
% \begin{macro}{\@@_backend_link_minima:}
% \begin{macro}{\@@_backend_link_outerbox:n}
% \begin{macro}{\@@_backend_link_sf_save:, \@@_backend_link_sf_restore:}
%   Links are created like annotations but with dedicated code to allow for
%   adjusting the size of the rectangle. In contrast to \pkg{hyperref}, we
%   grab the link content as a box which can then unbox: this allows the same
%   interface as for \pdfTeX{}.
%
%   Notice that the link setup here uses |/Action| not |/A|. That is because
%   Distiller \emph{requires} this trigger word, rather than a \enquote{raw}
%   PDF dictionary key (Ghostscript can handle either form).
%
%   Taking the idea of |evenboxes| from \pkg{hypdvips}, we implement a minimum
%   box height and depth for link placement. This means that \enquote{underlining}
%   with a hyperlink will generally give an even appearance. However, to ensure
%   that the full content is always above the link border, we do not allow
%   this to be negative (contrast \pkg{hypdvips} approach). The result should
%   be similar to \pdfTeX{} in the vast majority of foreseeable cases.
%
%   The object number for a link is saved separately from the rest of the
%   dictionary as this allows us to insert it just once, at either an
%   unbroken link or only in the first line of a broken one. That makes the
%   code clearer but also avoids a low-level PostScript error with the code
%   as taken from \pkg{hypdvips}.
%
%   Getting the outer dimensions of the text area may be better using a two-pass
%   approach and |\tex_savepos:D|. That plus generic mode are still to re-examine.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_begin_goto:nnw #1#2
  {
    \@@_backend_link_begin:nw
      { #1 /Subtype /Link /Action << /S /GoTo /D ( #2 ) >> }
  }
\cs_new_protected:Npn \@@_backend_link_begin_user:nnw #1#2
  { \@@_backend_link_begin:nw {#1#2} }
\cs_new_protected:Npn \@@_backend_link_begin:nw #1
  {
    \bool_if:NF \g_@@_backend_link_bool
      { \@@_backend_link_begin_aux:nw {#1} }
  }
%    \end{macrocode}
%   The definition of |pdfannot.link.dict| here is needed as there is code in the
%   PostScript headers for breaking links, and that can only work with this
%   available.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_begin_aux:nw #1
  {
    \bool_gset_true:N \g_@@_backend_link_bool
    \__kernel_backend_postscript:n
      { /pdfannot.link.dict ( #1 ) def }
    \tl_gset:Nn \g_@@_backend_link_dict_tl {#1}
    \@@_backend_link_sf_save:
    \mode_if_math:TF
      { \bool_gset_true:N \g_@@_backend_link_math_bool }
      { \bool_gset_false:N \g_@@_backend_link_math_bool }
    \hbox_set:Nw \l_@@_backend_content_box
      \@@_backend_link_sf_restore:
      \bool_if:NT \g_@@_backend_link_math_bool
        { \c_math_toggle_token }
  }
\cs_new_protected:Npn \@@_backend_link_end:
  {
    \bool_if:NT \g_@@_backend_link_bool
      { \@@_backend_link_end_aux: }
  }
\cs_new_protected:Npn \@@_backend_link_end_aux:
  {
      \bool_if:NT \g_@@_backend_link_math_bool
        { \c_math_toggle_token }
      \@@_backend_link_sf_save:
    \hbox_set_end:
    \@@_backend_link_minima:
    \hbox_set:Nn \l_@@_backend_model_box { Gg }
    \exp_args:Ne \@@_backend_link_outerbox:n
      {
        \int_if_odd:nTF { \value { page } }
          { \oddsidemargin }
          { \evensidemargin }
      }
    \box_move_down:nn { \box_dp:N \l_@@_backend_content_box }
      { \hbox:n { \__kernel_backend_postscript:n { pdfannot.save.linkll } } }
    \@@_backend_breaklink_postscript:n { pdfannot.bordertracking.begin }
    \@@_backend_breaklink_usebox:N \l_@@_backend_content_box
    \@@_backend_breaklink_postscript:n { pdfannot.bordertracking.end }
    \box_move_up:nn { \box_ht:N \l_@@_backend_content_box }
      {
        \hbox:n
          { \__kernel_backend_postscript:n { pdfannot.save.linkur } }
      }
    \int_gincr:N \g_@@_backend_int
    \int_gset_eq:NN \g_@@_backend_link_int \g_@@_backend_int
    \__kernel_backend_postscript:e
      {
        mark
        /_objdef { pdfannot \int_use:N \g_@@_backend_link_int }
        \g_@@_backend_link_dict_tl \c_space_tl
        pdfannot.rect
        /ANN ~ \l_@@_backend_breaklink_pdfmark_tl
      }
    \@@_backend_link_sf_restore:
    \bool_gset_false:N \g_@@_backend_link_bool
  }
\cs_new_protected:Npn \@@_backend_link_minima:
  {
    \hbox_set:Nn \l_@@_backend_model_box { Gg }
    \__kernel_backend_postscript:e
      {
        /pdfannot.linkdp.pad ~
          \dim_to_decimal:n
            {
              \dim_max:nn
                {
                    \box_dp:N \l_@@_backend_model_box
                  - \box_dp:N \l_@@_backend_content_box
                }
                { 0pt }
            } ~
              pdfannot.pt.dvi ~ def
        /pdfannot.linkht.pad ~
          \dim_to_decimal:n
            {
              \dim_max:nn
                {
                    \box_ht:N \l_@@_backend_model_box
                  - \box_ht:N \l_@@_backend_content_box
                }
                { 0pt }
            } ~
              pdfannot.pt.dvi ~ def
      }
  }
\cs_new_protected:Npn \@@_backend_link_outerbox:n #1
  {
    \__kernel_backend_postscript:e
      {
        /pdfannot.outerbox
          [
            \dim_to_decimal:n {#1} ~
            \dim_to_decimal:n { -\box_dp:N \l_@@_backend_model_box } ~
            \dim_to_decimal:n { #1 + \textwidth } ~
            \dim_to_decimal:n { \box_ht:N \l_@@_backend_model_box }
          ]
          [ exch { pdfannot.pt.dvi } forall ] def
        /pdfannot.baselineskip ~
          \dim_to_decimal:n { \tex_baselineskip:D } ~ dup ~ 0 ~ gt
            { pdfannot.pt.dvi ~ def }
            { pop ~ pop }
          ifelse
      }
  }
\cs_new_protected:Npn \@@_backend_link_sf_save:
  {
    \int_gset:Nn \g_@@_backend_link_sf_int
      {
        \mode_if_horizontal:TF
          { \tex_spacefactor:D }
          { 0 }
      }
  }
\cs_new_protected:Npn \@@_backend_link_sf_restore:
  {
    \mode_if_horizontal:T
      {
        \int_compare:nNnT \g_@@_backend_link_sf_int > { 0 }
          { \int_set:Nn \tex_spacefactor:D \g_@@_backend_link_sf_int }
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% Hooks to allow link breaking: something will be needed in format mode
% at some stage. At present this code is disabled, pending a decision to
% activate.
%    \begin{macrocode}
\use_none:nnn
\cs_if_exist:NT \hook_gput_code:nnn
  {
    \hook_gput_code:nnn { build/column/after } { backend }
      {
        \box_if_empty:NF \l_shipout_box
          {
            \vbox_set:Nn \l_shipout_box
              {
                \__kernel_backend_postscript:n
                  {
                    pdfannot.globaldict /pdfannot.brokenlink.rect ~ known
                      { pdfannot.bordertracking.continue }
                    if
                  }
                \vbox_unpack_drop:N \l_shipout_box
                \__kernel_backend_postscript:n
                  { pdfannot.bordertracking.endpage }
              }
          }
      }
    \tl_set:Nn \l_@@_backend_breaklink_pdfmark_tl { pdfannot.pdfmark }
    \cs_set_eq:NN \@@_backend_breaklink_postscript:n
      \__kernel_backend_postscript:n
    \cs_set_eq:NN \@@_backend_breaklink_usebox:N \hbox_unpack:N
  }
%    \end{macrocode}
%
% \begin{macro}{\@@_backend_link_last:}
%   The same as annotations, but with a custom integer.
%    \begin{macrocode}
\cs_new:Npn \@@_backend_link_last:
  { { pdfannot.annot \int_use:N \g_@@_backend_link_int } }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_margin:n}
%   Convert to big points and pass to PostScript.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_margin:n #1
  {
    \__kernel_backend_postscript:e
      {
        /pdfannot.linkmargin { \dim_to_decimal:n {#1} ~ pdfannot.pt.dvi } def
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_on:, \@@_backend_link_off:}
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_on:  { }
\cs_new_protected:Npn \@@_backend_link_off: { }
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
%</dvips>
%    \end{macrocode}
%
% \subsection{\LuaTeX{} and \pdfTeX{} backend}
%
%    \begin{macrocode}
%<*luatex|pdftex>
%    \end{macrocode}
%
% \begin{macro}{\@@_backend_generic:nnnn}
%   Simply pass the raw data through, just dealing with evaluation of dimensions.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_generic:nnnn #1#2#3#4
  {
%<*luatex>
    \tex_pdfextension:D annot ~
%</luatex>
%<*pdftex>
    \tex_pdfannot:D
%</pdftex>
      width  ~ \dim_eval:n {#1} ~
      height ~ \dim_eval:n {#2} ~
      depth  ~ \dim_eval:n {#3} ~
      {#4}
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_backend_last:}
%   A tiny amount of extra data gets added here; we use \texttt{e}-type
%   expansion to get the space in the right place and form. The \enquote{extra}
%   space in the \LuaTeX{} version is \emph{required} as it is consumed in
%   finding the end of the keyword.
%    \begin{macrocode}
\cs_new:Npe \@@_backend_last:
  {
    \exp_not:N \int_value:w
%<*luatex>
      \exp_not:N \tex_pdffeedback:D lastannot ~
%</luatex>
%<*pdftex>
      \exp_not:N \tex_pdflastannot:D
%</pdftex>
      \c_space_tl 0 ~ R
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}
%   {\@@_backend_link_begin_goto:nnw, \@@_backend_link_begin_user:nnw}
% \begin{macro}{\@@_backend_link_begin:nnnw}
% \begin{macro}{\@@_backend_link_end:}
%   Links are all created using the same internals.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_begin_goto:nnw #1#2
  { \@@_backend_link_begin:nnnw {#1} { goto~name } {#2} }
\cs_new_protected:Npn \@@_backend_link_begin_user:nnw #1#2
  { \@@_backend_link_begin:nnnw {#1} { user } {#2} }
\cs_new_protected:Npn \@@_backend_link_begin:nnnw #1#2#3
  {
%<*luatex>
    \tex_pdfextension:D startlink ~
%</luatex>
%<*pdftex>
    \tex_pdfstartlink:D
%</pdftex>
      attr {#1}
      #2 {#3}
  }
\cs_new_protected:Npn \@@_backend_link_end:
  {
%<*luatex>
    \tex_pdfextension:D endlink \scan_stop:
%</luatex>
%<*pdftex>
    \tex_pdfendlink:D
%</pdftex>
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_last:}
%   Formatted for direct use.
%    \begin{macrocode}
\cs_new:Npe \@@_backend_link_last:
  {
    \exp_not:N \int_value:w
%<*luatex>
      \exp_not:N \tex_pdffeedback:D lastlink ~
%</luatex>
%<*pdftex>
      \exp_not:N \tex_pdflastlink:D
%</pdftex>
      \c_space_tl 0 ~ R
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_margin:n}
%   A simple task: pass the data to the primitive.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_margin:n #1
  {
%<*luatex>
    \tex_pdfvariable:D linkmargin
%</luatex>
%<*pdftex>
    \tex_pdflinkmargin:D
%</pdftex>
      \dim_eval:n {#1} \scan_stop:
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_on:, \@@_backend_link_off:}
%   Separate definitions for the two engines.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_on:
%<*luatex>
  { \tex_pdfextension:D linkstate 0 ~ }
%</luatex>
%<*pdftex>
   { \tex_pdfrunninglinkon:D }
%</pdftex>
\cs_new_protected:Npn \@@_backend_link_off:
%<*luatex>
  { \tex_pdfextension:D linkstate 1 ~ }
%</luatex>
%<*pdftex>
  { \tex_pdfrunninglinkoff:D }
%</pdftex>
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
%</luatex|pdftex>
%    \end{macrocode}
%
% \subsection{\texttt{dvipdfmx} backend}
%
%    \begin{macrocode}
%<*dvipdfmx|xetex>
%    \end{macrocode}
%
% \begin{macro}{\@@_backend:n, \@@_backend:e}
%   A generic function for the backend PDF specials
%    \begin{macrocode}
\cs_new_protected:Npe \@@_backend:n #1
  { \__kernel_backend_literal:n { pdf: #1 } }
\cs_generate_variant:Nn \@@_backend:n { e }
%    \end{macrocode}
% \end{macro}
%
% \begin{variable}{\g_@@_backend_int}
%   Annotations are objects: but made with a separate tracker integer.
%    \begin{macrocode}
\int_new:N \g_@@_backend_int
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}{\@@_backend_generic:nnnn}
%   Simply pass the raw data through, just dealing with evaluation of dimensions.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_generic:nnnn #1#2#3#4
  {
    \int_gincr:N \g_@@_backend_int
    \@@_backend:e
      {
        ann ~ @pdfannot \int_use:N \g_@@_backend_int \c_space_tl
        width  ~ \dim_eval:n {#1} ~
        height ~ \dim_eval:n {#2} ~
        depth  ~ \dim_eval:n {#3} ~
        << /Type /Annot #4 >>
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_last:}
%    \begin{macrocode}
\cs_new:Npn \@@_backend_last:
  { @pdfannot \int_use:N \g_@@_backend_int }
%    \end{macrocode}
% \end{macro}
%
% \begin{variable}{\g_@@_backend_link_int}
%   To track annotations which are links.
%    \begin{macrocode}
\int_new:N \g_@@_backend_link_int
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}
%   {\@@_backend_link_begin_goto:nnw, \@@_backend_link_begin_user:nnw}
% \begin{macro}{\@@_backend_link_begin:n}
% \begin{macro}{\@@_backend_link_end:}
%   All created using the same internals.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_begin_goto:nnw #1#2
  {
    \@@_backend_link_begin:n
      { #1 /Subtype /Link /A << /S /GoTo /D ( #2 ) >> }
  }
\cs_new_protected:Npn \@@_backend_link_begin_user:nnw #1#2
  { \@@_backend_link_begin:n {#1#2} }
\cs_new_protected:Npe \@@_backend_link_begin:n #1
  {
    \int_gincr:N \exp_not:N \g_@@_backend_int
    \int_gset_eq:NN \exp_not:N \g_@@_backend_link_int
      \exp_not:N \g_@@_backend_int
    \@@_backend:e
      {
        bann ~
        @pdfannot
        \exp_not:N \int_use:N \exp_not:N \g_@@_backend_link_int
        \c_space_tl
        <<
          /Type /Annot
          #1
        >>
      }
  }
\cs_new_protected:Npn \@@_backend_link_end:
  { \@@_backend:n { eann } }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_last:}
%   Available using the backend mechanism with a suitably-recent
%   version.
%    \begin{macrocode}
\cs_new:Npn \@@_backend_link_last:
  { @pdfannot \int_use:N \g_@@_backend_link_int }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_margin:n}
%   Pass to \texttt{dvipdfmx}.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_margin:n #1
  { \__kernel_backend_literal:e { dvipdfmx:config~g~ \dim_eval:n {#1} } }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_on:, \@@_backend_link_off:}
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_on:  { \@@_backend:n { link } }
\cs_new_protected:Npn \@@_backend_link_off: { \@@_backend:n { nolink } }
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
%</dvipdfmx|xetex>
%    \end{macrocode}
%
% \subsection{\texttt{dvisvgm} backend}
%
%    \begin{macrocode}
%<*dvisvgm>
%    \end{macrocode}
%
% \begin{macro}{\@@_backend_generic:nnnn}
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_generic:nnnn #1#2#3#4 { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_backend_last:}
%    \begin{macrocode}
\cs_new:Npn \@@_backend_last: { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}
%   {\@@_backend_link_begin_goto:nnw, \@@_backend_link_begin_user:nnw}
% \begin{macro}{\@@_backend_link_begin:nnnw}
% \begin{macro}{\@@_backend_link_end:}
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_begin_goto:nnw #1#2 { }
\cs_new_protected:Npn \@@_backend_link_begin_user:nnw #1#2 { }
\cs_new_protected:Npn \@@_backend_link_begin:nnnw #1#2#3 { }
\cs_new_protected:Npn \@@_backend_link_end: { }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_last:}
%    \begin{macrocode}
\cs_new:Npe \@@_backend_link_last: { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_margin:n}
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_margin:n #1 { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_backend_link_on:, \@@_backend_link_off:}
%   For handling places like headers.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_backend_link_on:  { }
\cs_new_protected:Npn \@@_backend_link_off: { }
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
%</dvisvgm>
%    \end{macrocode}
%
% \subsection{Transitional code}
%
% This block is temporary: we have moved the backend functions here to a
% dedicated prefix. To facilitate that, we turn off DocStrip substitution
% and handle things manually.
%
%    \begin{macrocode}
%<@@=>
%    \end{macrocode}
%
%    \begin{macrocode}
\cs_new_eq:NN \__pdf_backend_annotation:nnnn \__pdfannot_backend_generic:nnnn
\cs_new_eq:NN \__pdf_backend_annotation_last: \__pdfannot_backend_last:
\clist_map_inline:nn
  {
    begin_goto:nnw ,
    begin_user:nnw ,
    begin:nnnw     ,
    end:           ,
    last:          ,
    margin:n
  }
  { \cs_new_eq:cc { __pdf_backend_link_ #1 } { __pdfannot_backend_link_ #1 } }
%    \end{macrocode}
%
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%
% \end{implementation}
%
% \PrintIndex