What are the correct HTML attributes to use for pre-selecting radio buttons in PHP forms for proper functionality?

When pre-selecting radio buttons in PHP forms, you can use the "checked" attribute in the input tag to specify which radio button should be selected by default. To do this, you need to dynamically generate the HTML code for the radio buttons in PHP and add the "checked" attribute to the input tag that corresponds to the pre-selected option. 

<form action="submit.php" method="post">
    <input type="radio" name="color" value="red" <?php if(isset($_POST['color']) && $_POST['color'] == 'red') echo 'checked'; ?>> Red
    <input type="radio" name="color" value="blue" <?php if(isset($_POST['color']) && $_POST['color'] == 'blue') echo 'checked'; ?>> Blue
    <input type="radio" name="color" value="green" <?php if(isset($_POST['color']) && $_POST['color'] == 'green') echo 'checked'; ?>> Green
    <input type="submit" value="Submit">
</form>

Keywords

HTML attributes radio buttons pre-selecting PHP forms functionality

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