[tex-live] why is VT (ascii 11) apparently "printable" with pdftex?

[jfbu]

Hi,

I have noticed that CTRL-I, CTRL-J and CTRL-K are "printable"

(cf http://tug.org/texinfohtml/web2c.html#TCX-files)

with pdfTeX or pdfLaTeX, by default.

Now Plain TeX has \catcode11 set to 7, but LaTeX has it to 15 making
it invalid by default. Also Plain TeX has \catcode1 set to 8, but CTRL-A
is not "printable".

This all looks a bit strange, why is ascii char 11 (VT = Unicode Line Tabulation)
handled this way ?

For test:

\the\catcode11
%\the\newlinechar

\immediate\write-1{^^K}

\begingroup
\catcode`@ 11
\def\x{\count@ 0
\loop
\catcode\count@ 12
\advance\count@ \@ne
\ifnum\count@<32
\repeat}\x%
\immediate\write-1{%
^^@^^A^^B^^C^^D^^E^^F^^G^^H^^I^^J^^K^^L^^M^^N^^O%
^^P^^Q^^R^^S^^T^^U^^V^^W^^X^^Y^^Z^^[^^\^^]^^^^^_}\endgroup
\bye

One can use -8bit option, then all are printable, the question is why
is VT printable by default ? 

(seems to contradict http://tug.org/texinfohtml/web2c.html#TCX-files,
and I can understand TAB and LF are considered a bit special)

Best,

Jean-François
PS: please keep me in CC if replying, thanks