 <p>Nope, <a href="http://php.net/manual/en/reserved.keywords.php" rel="nofollow">not possible</a>, at least not for class constants.</p> <blockquote> <p>You cannot use any of the following [reserved] words as constants, class names, function or method names.</p> </blockquote> <p>I don't know about C#, but there isn't any special symbol in PHP to transform a keyword into an identifier. As long as you don't name it exactly the same as a keyword (barring letter case), it'll just be any normal constant name.</p> <p>How about a (different since it's not just CSS) prefix? Gets repetitive to type, but is a nice workaround. I realize this may be redundant as well if your class is named something like <code>HTMLAttribute</code>, but it's the easiest way out.</p> <pre><code>const A_ID = 'id'; const A_CLASS = 'class'; // etc </code></pre>