Checking if a PHP Constant is Defined: The Ultimate Showdown Between `defined()` and `isset()`

How can you safely check if a constant defined with `define()` exists in PHP development? This article delves into the correct method using `defined()` and reveals why using `isset()` is a common pitfall. Through clear code examples and a comparative analysis, you'll master how to check for constant existence in PHP, avoiding unnecessary runtime notices and logical errors.