Are there any specific PHP libraries or functions that can help in displaying a form with error messages and retaining user input?

When displaying a form with error messages and retaining user input in PHP, you can use the `htmlspecialchars()` function to prevent XSS attacks and the `$_SERVER['PHP_SELF']` variable to submit the form to the current page. You can also use conditional statements to display error messages and retain user input using the `$_POST` superglobal array. 

<?php
// Check if form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate form data
    if (empty($_POST["username"])) {
        $error = "Username is required";
    } else {
        $username = htmlspecialchars($_POST["username"]);
    }
}
?>

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    <input type="text" name="username" value="<?php echo isset($username) ? $username : ''; ?>">
    <span><?php echo isset($error) ? $error : ''; ?></span>
    <button type="submit">Submit</button>
</form>

Keywords

form validation error messages user input retention PHP libraries input validation

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