Start of Line

<..TABLE tabbing..>+
 \def\:temp{%
    \TRD:tab  \gdef\loc:tab{\z@}%
    \ifnum \@nxttabmar >\@hightab
      \@badtab  \global\@nxttabmar \@hightab
    \fi
    \global\@curtabmar \@nxttabmar
    \global\@curtab \@curtabmar
    \global\setbox\@curline \hbox {}%
    \@startfield  <.indented tabs.>%
    \strut}
 \HLet\@startline=\:temp
 -_-_-

The \x:tab is needed for an extra field at the start when tabs start in middle of line (due to \+).

<..indented tabs..>
 \ifdim \the\dimen\@curtab > \z@
        \gdef\x:tab{\D:tab  \d:tab\gdef\x:tab{}}%
 \else  \gdef\x:tab{}%
 \fi
 -_-_-

The \’ command is ignored here, and the content is pushed to the next field.

<..TABLE tabbing..>+
 \def\:temp{%
   \@stopfield
   \global\setbox\@curline\hbox{%
     \box\@curline
     \hskip-\wd\@curfield \hskip-\tabbingsep
     <.move tab backward.>%
     \box\@curfield
     \hskip\tabbingsep}%
   \@startfield
   \ignorespaces}
 \HLet\@tablab=\:temp
 -_-_-

<..move tab backward..>
 \x:tab \D:tab
 -_-_-

<..TABLE tabbing..>+
 \def\:temp{%
   \@stopfield <.paused addfield.>%
   \global\advance\@tabpush \@ne
   \begingroup  \@contfield}
 \HLet\pushtabs=\:temp
 \def\:temp{\@stopfield <.paused addfield.>%
   \ifnum \@tabpush >\z@
     \endgroup  \global\advance\@tabpush \m@ne
     \ifnum \@curtab >\@hightab
       \global \@curtab \@hightab
       \@badtab \fi
   \else \@badpoptabs \fi
   \@contfield}
 \HLet\poptabs=\:temp
 -_-_-