pattern

A regular expression that the control's value is checked against. The pattern must match the entire value, not just some subset. Use the <strong>title</strong> attribute to describe the pattern to help the user. This attribute applies when the value of the <strong>type</strong> attribute is <code>text</code>, <code>search</code>, <code>tel</code>, <code>url</code>, <code>email</code>, or <code>password</code>, otherwise it is ignored. The regular expression language is the same as JavaScript <a title="The RegExp constructor creates a regular expression object for matching text with a pattern." href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp"><code>RegExp</code></a> algorithm, with the <code>'u'</code> parameter that makes it treat the pattern as a sequence of unicode code points. The pattern is not surrounded by forward slashes.