What are the common pitfalls to avoid when modifying PHP code in a template file?

One common pitfall to avoid when modifying PHP code in a template file is directly modifying core theme files, as this can lead to issues during theme updates. Instead, it is recommended to use child themes or custom template files to make modifications. Additionally, it's important to properly sanitize and validate user input to prevent security vulnerabilities.

// Example of using a child theme to modify PHP code in a template file
function my_theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
    wp_enqueue_style( 'child-style', get_stylesheet_directory_uri() . '/style.css', array( 'parent-style' ) );
}
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );