LaTeX: To correct the engine detection of expl3 in using pLaTeX

bxexpl3ptex.sty

% bxexpl3ptex.sty

%% package declaration
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxexpl3ptex}[2015/07/28 v0.3]

%% hack for \ifpdfprimitive
\let\bxqxp@postproc\relax
\expandafter\ifx\csname ifpdfprimitive\endcsname\relax
  \expandafter\@firstofone
\else \expandafter\@gobble
\fi {%
  \let\bxqxp@ifpdfprimitive\ifpdfprimitive
  \let\ifpdfprimitive\ifdefined
  \def\bxqxp@postproc{%
    \let\ifpdfprimitive\bxqxp@ifpdfprimitive
    \let\bxqxp@ifpdfprimitive\@undefined
    \let\bxqxp@postproc\relax
  }%
}

%% do it
\RequirePackageWithOptions{expl3}
\bxqxp@postproc
\ExplSyntaxOn

%--------------------------------------- adjustments

\cs_new_eq:NN \ptex_if_engine:T    \use_none:n
\cs_new_eq:NN \ptex_if_engine:F    \use:n
\cs_new_eq:NN \ptex_if_engine:TF   \use_ii:nn
\cs_new_eq:NN \ptex_if_engine_p:   \c_false_bool
\cs_new_eq:NN \uptex_if_engine:T   \use_none:n
\cs_new_eq:NN \uptex_if_engine:F   \use:n
\cs_new_eq:NN \uptex_if_engine:TF  \use_ii:nn
\cs_new_eq:NN \uptex_if_engine_p:  \c_false_bool

\str_if_eq_x:nnT { \token_to_meaning:N \kanjiskip }
  { \token_to_str:N \kanjiskip }
  {
    % I'm pTeX! The current judge is:
    %   pdftex_if_engine = true
    %   luatex_if_engine = false
    %   xetex_if_engine  = false
    \cs_gset_eq:NN \ptex_if_engine:T    \use:n
    \cs_gset_eq:NN \ptex_if_engine:F    \use_none:n
    \cs_gset_eq:NN \ptex_if_engine:TF   \use_i:nn
    \cs_gset_eq:NN \ptex_if_engine_p:   \c_true_bool
    % I'm not pdfTeX.
    \cs_gset_eq:NN \pdftex_if_engine:T  \use_none:n
    \cs_gset_eq:NN \pdftex_if_engine:F  \use:n
    \cs_gset_eq:NN \pdftex_if_engine:TF \use_ii:nn
    \cs_gset_eq:NN \pdftex_if_engine_p: \c_false_bool
  }

\str_if_eq_x:nnT { \token_to_meaning:N \forcecjktokens }
  { \token_to_str:N \forcecjktokens }
  {
    % I'm upTeX!
    \cs_gset_eq:NN \uptex_if_engine:T   \use:n
    \cs_gset_eq:NN \uptex_if_engine:F   \use_none:n
    \cs_gset_eq:NN \uptex_if_engine:TF  \use_i:nn
    \cs_gset_eq:NN \uptex_if_engine_p:  \c_true_bool
  }

%--------------------------------------- done
\ExplSyntaxOff
\endinput
%% EOF

Usage

• Load this package instead of expl3. This package loads internally expl3, passing all the given options.
• If there is a package that internally loads expl3, then load this package before such package.

How to use the media9 package on pLaTeX + dvipdfmx:

\documentclass[...,dvipdfmx]{article}
\usepackage{bxexpl3ptex}% at the beginning of preamble
\usepackage{media9}