 text that does not match any rules? For example in Lua, the &lsquo;!&rsquo;
    character is meaningless outside a string or comment. Normally the lexer
    skips over such text. If instead you want to highlight these &ldquo;syntax errors&rdquo;,
    add an additional end rule:</p>

    <pre><code>
    lex:add_rule('whitespace', ws)
    ...
    lex:add_rule('error', token(lexer.ERROR, lexer.any))
    </code></pre>

    <p>This identifies and highlights any character not matched by an existing
    rule as a