pattern attribute

Explanation

Pattern attribute allows the user to place a pattern which can be matched by the value entered by user before the field is submitted.

Example Code:

<form action="demo4.php">
  Enter login code: <input type="text" name="code" pattern="[A-Za-z]{5}" title="Five letter code" />
  <input type="submit" />
</form>

Result :

User can enter only the "alphabetical characters".
The value entered by user will be validated only when it matches the required value.
It is used to do regular expression i.e. to specify the pattern characters.