We need the \HTable{...} version for handling TeX tables and for not modifying ‘&’ with other catcode or replacement command. Otherwise, \HTable...\EndHtable are better because that don’t ask for expandable stuff.
<..HTable..>
\def\HTable{%
\let\:TR=\empty
\let\TABLE:=\empty
\futurelet\:temp\T:ABLE}
-_-_-
Defining the \HTable in terms of \halign is problematic for a few reasons.
[??]
Also, do we have consistent behavior between TeX and LaTeX here?