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<h1>The input pattern attribute</h1>
<p>The pattern attribute specifies a regular expression that the input element's value is checked against.</p>
<form action="/action_page.php">
<label for="country_code">Country code:</label>
<input type="text" id="country_code" name="country_code" pattern="[A-Za-z]{3}" title="Three letter country code"><br><br>
<input type="submit" value="Submit">
</form>
</body>
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