Scanner/Parser question - what does _P imply?

I can't find an authoritative answer to this question.<br /><br /> Many of the keywords listed in keywords.c are
definedwith symbolic names that end in '_P' (underscore P).<br /><br /> What differentiates those keywords from the
otherkeywords?  What does the 'P' stand for?<br /><br /> Are those PostgreSQL-specific keywords (i.e. keywords not
definedby the SQL standard)?<br /><br /> Thanks.<br /><br /><br />            -- Korry<br /><table cellpadding="0"
cellspacing="0"width="100%"><tr><td><br /><br /> --<br />   Korry Douglas    <a
href="mailto:korryd@enterprisedb.com">korryd@enterprisedb.com</a><br/>   EnterpriseDB      <a
href="http://www.enterprisedb.com">http://www.enterprisedb.com</a></td></tr></table>