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Title=.fail

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Generates an error or a warning.  If the value of the <I>expression</I> is 500
or more, <CODE>as</CODE> will print a warning message.  If the value is less
than 500, <CODE>as</CODE> will print an error message.  The message will
include the value of <I>expression</I>.  This can occasionally be useful inside
complex nested macros or conditional assembly.
