multline

The environment of AmsLaTeX are being scanned as parameters of \collect@@body. Hence, the featured of TeX4ht introduced to \halign are nulled there.

<..equations of amsmath.sty..>+
                                     \catcode‘\#=13 \catcode‘\!=6
 \def\reg:multline!1{%
   <.inany@true.>    \Let@
   \@display@init{\global\advance\row@\@ne \global\dspbrk@lvl\m@ne}%
   <.displaybreak@.>    \restore@math@cr    \let\tag\tag@in@align
   \global\tag@false \global\let\raise@tag\@empty    \mmeasure@{#1}%
   \let\tag\gobble@tag <.multline label.>%
   <.halign amsmath multline.>}
                                     \catcode‘\#=6 \catcode‘\!=12
 -_-_-

<..halign amsmath multline..>
 \ifst@rred
   \expandafter\let\csname e:multline*\endcsname=\empty
   \expandafter\let\csname f:multline*\endcsname=\empty
 \fi
 \SaveMkHalignConf:g{multline\ifst@rred *\fi}\HRestore\noalign
 \MkHalign#{\hbox{$\m@th\displaystyle<.sub/sup base.>#$}}!1%
 -_-_-

<..multline label..>
 \ifst@rred  \let\label\@gobble  \else
    \stepcounter{equation}%
    \def\label{\let\cnt:currentlabel\@currentlabel
       \def\:@currentlabel{\ifx \cnt:currentlabel\@currentlabel
       \the\c@equation\else \@currentlabel\fi}%
       \anc:lbl r{equation}\ltx@label}%
    \edef\@currentlabel{\the\c@equation}%
 \fi
 -_-_-

<..multline tag..>
 \ifst@rred\else
    \e:multline\csname a:multline-num\endcsname
    \tagform@\theequation\csname b:multline-num\endcsname\f:multline
 \fi
 -_-_-

<..equations of amsmath.sty..>+
 \def\:tempc{<.multline tag.>\math@cr \EndMkHalign
    \RecallMkHalignConfig \csname b:multline\ifst@rred *\fi\endcsname
    $$\global\@ignoretrue  }
 \HLet\endmultline=\:tempc
 \def\:tempc{\pic:MkHalign{multline\ifst@rred *\fi}}
 \HLet\multline@=\:tempc
 \NewConfigure{multline}{6}
 \NewConfigure{multline-num}{2}
 \@xp\let\csname reg:multline*\endcsname=\reg:multline
 \@xp\let\csname endmultline*\endcsname=\endmultline
 \NewConfigure{multline*}{4}
 -_-_-