Hello,
Testing out how \lastnamedcs and \begincsname behave for some LaTeX
kernel work, the following has come up:
\def\test#1{%
\expandafter\def\csname #1\endcsname{abc}
\message{\begincsname #1\endcsname}}
\test{x}
\test{y}
\test{}
\expandafter\let\expandafter\x\csname abc\endcsname
\show\x
\expandafter\show\lastnamedcs a
\expandafter\let\expandafter\x\csname hbox\endcsname
\show\x
\expandafter\show\lastnamedcs b
\expandafter\let\expandafter\x\csname\endcsname
\show\x
\expandafter\show\lastnamedcs c
\end
As you'll see, with an empty csname, both \lastnamedcs and \begincsname
give (possibly) surprising results. Is this by-design?
Joseph