Improve S5869 (duplicates-in-character-class): Mention character cl…

…ass escapes (#4331)

sonar-plugin/javascript-checks/src/main/resources/org/sonar/l10n/javascript/rules/javascript/S5869.html

@@ -7,14 +7,31 @@ <h2>Why is this an issue?</h2>
 mistake is trying to use a range like <code>[0-99]</code> to match numbers of up to two digits, when in fact it is equivalent to <code>[0-9]</code>.
 Another common cause is forgetting to escape the <code>-</code> character, creating an unintended range that overlaps with other characters in the
 character class.</p>
-<h3>Noncompliant code example</h3>
-<pre>
+<p>Character ranges can also create duplicates when used with character class escapes. These are a type of escape sequence used in regular expressions
+to represent a specific set of characters. They are denoted by a backslash followed by a specific letter, such as <code>\d</code> for digits,
+<code>\w</code> for word characters, or <code>\s</code> for whitespace characters. For example, the character class escape <code>\d</code> is
+equivalent to the character range <code>[0-9]</code>, and the escape <code>\w</code> is equivalent to <code>[a-zA-Z0-9_]</code>.</p>
+<h2>How to fix it</h2>
+<p>Remove the extra character, character range, or character class escape.</p>
+<h3>Code examples</h3>
+<h4>Noncompliant code example</h4>
+<pre data-diff-id="1" data-diff-type="noncompliant">
 /[0-99]/ // Noncompliant, this won't actually match strings with two digits
 /[0-9.-_]/ // Noncompliant, .-_ is a range that already contains 0-9 (as well as various other characters such as capital letters)
+/[a-z0-9\d]/ // Noncompliant, \d matches a digit and is equivalent to [0-9]
 </pre>
-<h3>Compliant solution</h3>
-<pre>
+<h4>Compliant solution</h4>
+<pre data-diff-id="1" data-diff-type="compliant">
 /[0-9]{1,2}/
 /[0-9.\-_]/
+/[a-z\d]/
 </pre>
+<h2>Resources</h2>
+<h3>Documentation</h3>
+<ul>
+  <li> MDN web docs - <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions/Character_classes">Character
+  classes</a> </li>
+  <li> MDN web docs - <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class_escape">Character
+  class escape</a> </li>
+</ul>