ag Values</A> </h2>

<p>After DEFINE-ing a flag, you may optionally register a validator
function with the flag.  If you do this, after the flag is parsed from
the commandline, and whenever its value is changed via a call to
<code>SetCommandLineOption()</code>, the validator function is called
with the new value as an argument.  The validator function should
return 'true' if the flag value is valid, and false otherwise.
If the function returns false for the new setting of the
flag, the flag will retain its 