Hi guys.

Readline goes to commendable efforts to disable all tty special characters 
whose default values clash with default readline bindings - all except STOP 
(^S) XON/XOFF flow control, which clashes with readline's default binding for 
forward-search-history. This issue was previously raised in this list in
https://mail.gnu.org/archive/html/bug-bash/2020-11/msg00046.html. Chet added 
the requested code in readline 8.2 under control of the USE_XON_XOFF macro, 
albeit disabled by default. He then modified it in readline 8.3 so it is now 
under control of the variable _rl_use_tty_xon_xoff instead of USE_XON_XOFF. 
Regardless, the new functionality still remains disabled in both master and 
devel versions.

Why can it not just be enabled by default? That would deliver the greatest good 
for the greatest number.  As it currently stands, any novice user who attempts 
to use forward-search-history as per bash/readline documentation, or who hits 
^S by accident in bash, will find the display mysteriously frozen, with no 
guidance from bash/readline docs as to why. This to me is a far bigger problem 
than the possibility of breaking changes. XON/XOFF tty special characters 
represent interactive functionality, so the only scripts that could conceivably 
be broken by such a change probably deserve to be broken. After all, what use 
is a frozen terminal for an interactive shell? XON/XOFF is undeniably useful 
for logorrheic terminal applications so one would not want to disable it 
altogether, but it is downright pathological for bash.
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