tion is usually straightforward, there are a number of
subtleties that may need emphasizing.  For example, since spaces are deemed to
be irrelevant when they come between tokens in the input for most languages,
one should not attempt to declare literal tokens that have spaces within
them.</P>

<P>The grammar for tokens allows for empty right-hand sides.  This may seem
strange, especially as no scanner is generated if the right-hand side of a
declaration is missing.  This facility is used if the user wishes 