add plug for mbox in math

CHANGELOG.md

@@ -7,6 +7,8 @@ this project uses date-based 'snapshot' version identifiers.
 ## [Unreleased]
 
 ### Changed
+- Ulrike Fischer, 2024-03-03
+  luamml.dtx: add plug for mbox socket to correctly annotate them in math.
 
 - Ulrike Fischer, 2024-11-29
   luamml-structelemwriter.lua: use structnum instead of label when stashing. 

luamml.dtx

@@ -523,7 +523,47 @@
 %    \end{macrocode}
 % \end{macro}
 %
+% \subsection{Sockets}
+% In various places luamml has to add code to kernel commands. This is done through
+% sockets which are predeclared in lttagging.
 %
+% \subsubsection{mbox}
+% This socket annotates an \cs{mbox} inside math.
+% We test for the socket until the release 2025-06-01.
+%    \begin{macrocode}
+\str_if_exist:cF { l__socket_tagsupport/math/luamml/mbox_plug_str }
+ {
+   \NewSocket{tagsupport/math/luamml/mbox}{2}
+   \NewSocketPlug{tagsupport/math/luamml/mbox}{default}{#2}
+   \AssignSocketPlug{tagsupport/math/luamml/mbox}{default}
+ }
+%<*luatex>
+\NewSocketPlug{tagsupport/math/luamml/mbox}{luamml}
+ {
+   \bool_lazy_and:nnTF
+    { \mode_if_math_p: }
+    { \int_if_odd_p:n { \int_div_truncate:nn { \l__luamml_flag_int } { 8 } } }
+    {
+      \tag_struct_begin:n
+       {
+         tag=mtext,
+         stash,
+       }
+      \tag_mc_begin:n {}
+      \luamml_annotate:en
+       {
+         nucleus = true,
+         structnum=\tag_get:n{struct_num}
+       }
+       { #2 }
+      \tag_mc_end:
+      \tag_struct_end:
+    }
+    { #2 }
+  }
+\AssignSocketPlug{tagsupport/math/luamml/mbox}{luamml}
+%</luatex>
+%    \end{macrocode}
 % \subsection{Patching}
 % For some packages, we ship with patches to make them more compatible and to
 % demonstrate how other code can be patched to work with \texttt{luamml}.