Custom Fields in WordPress Plugins — a practical guide to WordPress custom fields with clear examples you can reuse in real projects.
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Short description
Custom fields store values in postmeta. Prefer uniquely prefixed meta keys.
Save meta
update_post_meta($post_id, '_acme_isbn', sanitize_text_field($isbn));
$isbn = get_post_meta($post_id, '_acme_isbn', true);