This is an example I built with w3schools test page:
<!DOCTYPE html>
<html>
<body>
<form onsubmit="getElementById('s').innerHTML=getElementById('i').value;return false;">
Country code: <input id="i" type="text" name="country_code" pattern="([a-zA-Z0-9]| |/|\\|@|#|\$|%|&)+" title="Three letter country code">
<input type="submit">
</form>
<p>Submitted value: <span id="s">
Note: The pattern attribute of the input tag is not supported in Internet Explorer 9 and earlier versions, or in Safari.
You can use it to make your own tests at http://www.w3schools.com/tags/tryit.asp?filename=tryhtml5_input_pattern