What are common syntax errors that can occur when mixing PHP and HTML code?

One common syntax error that can occur when mixing PHP and HTML code is forgetting to properly close PHP tags before switching back to HTML code. This can lead to unexpected results or errors in the output. To solve this issue, always make sure to close PHP tags before entering HTML code and vice versa.

<?php
// Correct way to mix PHP and HTML code
?>
<!DOCTYPE html>
<html>
<head>
    <title>PHP and HTML</title>
</head>
<body>
    <h1><?php echo "Hello, World!"; ?></h1>
</body>
</html>
<?php
// Resume PHP code here
?>