[pdftex] features request 2

[Linas Stonys]

Hi,
from time to time I face the problem where I need to do something inside 
tex group (simple group or box or table cell)
or to mark up some content with tex4ht tags ( or tagging pdf )
and sometimes \aftergroup is not enough.   So I would like to ask about 
new token or token list which would
be inserted before current group end (\beforeendgroup).


EXAMPLE:
\showboxdepth=\maxdimen
\showboxbreadth=\maxdimen
b
\hbox{x\aftergroup d  x}
c
\showlists

LOG OUTPUT:
\tenrm b
\glue(\spaceskip) 3.33333 plus 1.66666 minus 1.11111
\hbox(4.30554+0.0)x13.88893, direction TLT
.\tenrm x
.\glue(\spaceskip) 3.33333 plus 1.66666 minus 1.11111
.\tenrm x
\tenrm d
\glue(\spaceskip) 3.33333 plus 1.66666 minus 1.11111
\tenrm c


COULD BE:
b
\hbox{x\beforeendgroup d  x}
c
\showlists

LOG OUTPUT:
\tenrm b
\glue(\spaceskip) 3.33333 plus 1.66666 minus 1.11111
\hbox(4.30554+0.0)x13.88893, direction TLT
.\tenrm x
.\glue(\spaceskip) 3.33333 plus 1.66666 minus 1.11111
.\tenrm x
.\tenrm d
\tenrm c

Of course here needs to think about several same macros how they should 
queue the content.

Thanks in advance,
Linas