What are some common pitfalls when using regular expressions in PHP, especially when searching for specific patterns like "<<D<<", "<<N<<", etc. in a textarea field?

One common pitfall when using regular expressions in PHP to search for specific patterns like "<<D<<" or "<<N<<" in a textarea field is not properly escaping special characters. To search for these patterns accurately, you need to escape the special characters in the pattern using preg_quote() function. This ensures that the pattern is treated as a literal string and not as a regular expression metacharacter.

// Example code snippet to search for "<<D<<" in a textarea field with proper escaping of special characters
$text = $_POST['textarea_field']; // Assuming the textarea field is submitted via POST
$pattern = '/'.preg_quote('<<D<<', '/').'/'; // Escape special characters in the pattern
if (preg_match($pattern, $text)) {
    echo "Pattern found in the textarea field!";
} else {
    echo "Pattern not found.";
}