[NTG-context] Minimal code for exporting custom tags

[Aditya Mahajan]

On Tue, 19 May 2020, Aditya Mahajan wrote:

> On Mon, 18 May 2020, Aditya Mahajan wrote:
>
>>> Thanks! This also helped me find the documentation in hybrid.pdf.
>
> Also epub-mkiv.pdf. Not sure why I didn't think of looking there.
>
>> How do I pass options so that the export is
>>
>> <mycommand name=whatever>...</mycommand>
>>
>> (or some variant of that). I thought that
>>
>> \startelement[mycommand][name=whatever]
>>
>> should work (there are some such examples in the texmf tree), but it does 
>> not.
>
> epub-mkiv.pdf states that I need `\setupexport[properties=yes]`, but that 
> doesn't work either:

There is a bug in back-exp.lua:

--- /tmp/back-exp.lua	2020-05-19 02:13:54.961276226 -0400
+++ /opt/luametatex/texmf-context/tex/context/base/mkiv/back-exp.lua	2020-05-19 02:13:01.687385009 -0400
@@ -2305,8 +2305,10 @@
                  if not p then
                      -- skip
                  elseif exportproperties == v_yes then
+                    n = n+1
                      r[n] = attributes(p)
                  else
+                    n = n+1
                      r[n] = properties(p)
                  end
              end

Patching this fixes the export.

Aditya