typo

regular-expressions.html

@@ -90,7 +90,7 @@ body{counter-reset:h1 5}
 <li>The tens characters (<code>I</code>, <code>X</code>, <code>C</code>, and <code>M</code>) can be repeated up to three times. At <code>4</code>, you need to subtract from the next highest fives character. You can&#8217;t represent <code>4</code> as <code>IIII</code>; instead, it is represented as <code>IV</code> (&#8220;<code>1</code> less than <code>5</code>&#8221;). The number <code>40</code> is written as <code>XL</code> (<code>10</code> less than <code>50</code>), <code>41</code> as <code>XLI</code>, <code>42</code> as <code>XLII</code>, <code>43</code> as <code>XLIII</code>, and then <code>44</code> as <code>XLIV</code> (<code>10</code> less than <code>50</code>, then <code>1</code> less than <code>5</code>).
 <li>Similarly, at <code>9</code>, you need to subtract from the next highest tens character: <code>8</code> is <code>VIII</code>, but <code>9</code> is <code>IX</code> (<code>1</code> less than <code>10</code>), not <code>VIIII</code> (since the <code>I</code> character can not be repeated four times). The number <code>90</code> is <code>XC</code>, <code>900</code> is <code>CM</code>.
 <li>The fives characters can not be repeated. The number <code>10</code> is always represented as <code>X</code>, never as <code>VV</code>. The number <code>100</code> is always <code>C</code>, never <code>LL</code>.
-<li>Roman numerals are always written highest to lowest, and read left to right, so the order the of characters matters very much. <code>DC</code> is <code>600</code>; <code>CD</code> is a completely different number (<code>400</code>, <code>100</code> less than <code>500</code>). <code>CI</code> is <code>101</code>; <code>IC</code> is not even a valid Roman numeral (because you can&#8217;t subtract <code>1</code> directly from <code>100</code>; you would need to write it as <code>XCIX</code>, for <code>10</code> less than <code>100</code>, then <code>1</code> less than <code>10</code>).
+<li>Roman numerals are always written highest to lowest, and read left to right, so the order of characters matters very much. <code>DC</code> is <code>600</code>; <code>CD</code> is a completely different number (<code>400</code>, <code>100</code> less than <code>500</code>). <code>CI</code> is <code>101</code>; <code>IC</code> is not even a valid Roman numeral (because you can&#8217;t subtract <code>1</code> directly from <code>100</code>; you would need to write it as <code>XCIX</code>, for <code>10</code> less than <code>100</code>, then <code>1</code> less than <code>10</code>).
 </ul>
 <h3 id=thousands>Checking For Thousands</h3>
 <p>What would it take to validate that an arbitrary string is a valid Roman numeral?  Let&#8217;s take it one digit at a time. Since Roman numerals are always written highest to lowest, let&#8217;s start with the highest: the thousands place. For numbers 1000 and higher, the thousands are represented by a series of <code>M</code> characters.