-When you specify this option, the compiler is built to perform checking
-of tree node types when referencing fields of that node, and some other
-internal consistency checks. This does not change the generated code,
-but adds error checking within the compiler. This will slow down the
-compiler and may only work properly if you are building the compiler
-with GCC@. This is on by default when building from CVS or snapshots,
-but off for releases. More control over the checks may be had by
-specifying @var{list}; the categories of checks available are
-@samp{misc}, @samp{tree}, @samp{gc}, @samp{rtl}, @samp{rtlflag},
-@samp{fold}, @samp{gcac} and @samp{valgrind}. The check @samp{valgrind}
-requires the external @command{valgrind} simulator, available from
-@uref{http://valgrind.kde.org/}. The default when @var{list} is
-not specified is @samp{misc,tree,gc,rtlflag}; the checks @samp{rtl},
-@samp{gcac} and @samp{valgrind} are very expensive.
+When you specify this option, the compiler is built to perform internal
+consistency checks of the requested complexity. This does not change the
+generated code, but adds error checking within the compiler. This will
+slow down the compiler and may only work properly if you are building
+the compiler with GCC@. This is @samp{yes} by default when building
+from SVN or snapshots, but @samp{release} for releases. More control
+over the checks may be had by specifying @var{list}. The categories of
+checks available are @samp{yes} (most common checks
+@samp{assert,misc,tree,gc,rtlflag,runtime}), @samp{no} (no checks at
+all), @samp{all} (all but @samp{valgrind}), @samp{release} (cheapest
+checks @samp{assert,runtime}) or @samp{none} (same as @samp{no}).
+Individual checks can be enabled with these flags @samp{assert},
+@samp{fold}, @samp{gc}, @samp{gcac} @samp{misc}, @samp{rtl},
+@samp{rtlflag}, @samp{runtime}, @samp{tree}, and @samp{valgrind}.
+
+The @samp{valgrind} check requires the external @command{valgrind}
+simulator, available from @uref{http://valgrind.org/}. The
+@samp{rtl}, @samp{gcac} and @samp{valgrind} checks are very expensive.
+To disable all checking, @samp{--disable-checking} or
+@samp{--enable-checking=none} must be explicitly requested. Disabling
+assertions will make the compiler and runtime slightly faster but
+increase the risk of undetected internal errors causing wrong code to be
+generated.