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<html><body><form action="/action_page.php"> Facebook profile: <input type="url" id="myURL" name="fb"> <input type="submit"></form><p>Click the "Try it" button to specify a regular expression that the URL field's value will be checked against. Note that we also set the "title" to describe the pattern.</p><button onclick="myFunction()">Try it</button><p id="demo"></p><script>function myFunction() { document.getElementById("myURL").pattern = "http://www\.facebook\.com\/(.+)|https://www\.facebook\.com\/(.+)"; document.getElementById("myURL").title = "URL must start with http://www.facebook.com/"; document.getElementById("demo").innerHTML = "The URL field now only accept URL's that start with http://www.facebook.com/ or https://www.facebook.com/.";}</script></body></html>