The HTML pattern attribute specifies a regular expression that the value of the form control must match.
Definition and Usage
➔ If the pattern does not meet the constraints, the patternMismatch property will be true.
➔ The pattern attribute is used with text, telephone, email, URL, password, and search input types.
Example
<!DOCTYPE html>
<html>
<head>
<title>HTML pattern attribute Example</title>
</head>
<body>
<h3>HTML pattern attribute Example</h3>
<p>Type 4 uppercase or lowercase letters in the textfield to match the pattern and click Submit.</p>
<form action="#">
Country code:
<input type="text" id="codeId" name="code" pattern="[A-Za-z]{4}"
placeholder="4 letters in uppercase or lowercase." title="4 letters in uppercase or lowercase."><br><br>
<input type="submit">
</form>
</body>
</html>