Until now, we’ve known what custom fields is and how to use the functions provided by WordPress to work with custom fields. You’ve prepared everything needed to develop practical applications. But wait, before embarking on doing something new, you had better dig a bit deeper to have thorough understand custom fields' nature. It’s time to find out an answer to the question: “What really happens with custom fields when I click Save post?”. The two coming posts will give you the answers.