Add \markdownMode value 4

markdown.dtx

@@ -8307,10 +8307,10 @@ For more information, see the examples for the \Opt{finalizeCache} option.
 % \begin{markdown}
 %
 % The \mdef{markdownOptionInputTempFileName} macro sets the filename of the
-% temporary input file that is created during the conversion from markdown to
-% plain \TeX{} in \mref{markdownMode} other than `2`. It defaults to
-% \mref{jobname}`.markdown.in`. The same limitations as in the case of the
-% \mref{markdownOptionHelperScriptFileName} macro apply here.
+% temporary input file that is created during the buffering of markdown text
+% from a \TeX{} source. It defaults to \mref{jobname}`.markdown.in`. The same
+% limitations as in the case of the \mref{markdownOptionHelperScriptFileName}
+% macro apply here.
 %
 % \end{markdown}
 %  \begin{macrocode}
@@ -14397,6 +14397,7 @@ following text:
 % - `0` – Shell escape via the 18 output file stream
 % - `1` – Shell escape via the Lua \luamref{os.execute} method
 % - `2` – Direct Lua access
+% - `3` – The \pkg{lt3luabridge} Lua package
 %
 % By defining the macro, the user can coerce the package to use a specific mode.
 % If the user does not define the macro prior to loading the plain \TeX{}
@@ -14406,13 +14407,32 @@ following text:
 %
 % \end{markdown}
 %  \begin{macrocode}
-\ifx\markdownMode\undefined
-  \ifx\directlua\undefined
-    \def\markdownMode{0}%
-  \else
-    \def\markdownMode{2}%
-  \fi
-\fi
+\ExplSyntaxOn
+\cs_if_exist:NF
+  \markdownMode
+  {
+    \file_if_exist:nTF
+      { lt3luabridge.tex }
+      {
+        \cs_new:Npn
+          \markdownMode
+          { 4 }
+      }
+      {
+        \cs_if_exist:NTF
+          \directlua
+          {
+            \cs_new:Npn
+              \markdownMode
+              { 2 }
+          }
+          {
+            \cs_new:Npn
+              \markdownMode
+              { 0 }
+          }
+      }
+  }
 %    \end{macrocode}
 % \begin{markdown}
 %
@@ -14423,14 +14443,12 @@ following text:
 %
 % \end{markdown}
 %  \begin{macrocode}
-\ExplSyntaxOn
 \int_new:N
   \g__luabridge_method_int
 \int_gset:Nn
   \g__luabridge_method_int
   { \markdownMode }
 \ExplSyntaxOff
-\input l3luabridge\relax
 %    \end{macrocode}
 % \par
 % \begin{markdown}