How can PHP developers ensure their code is compatible with both PHP 4 and PHP 5 environments?

PHP developers can ensure their code is compatible with both PHP 4 and PHP 5 environments by avoiding the use of features or functions that are specific to PHP 5 and sticking to syntax and functions that are supported in both versions. They can also use conditional statements to check the PHP version and adjust the code accordingly. 

if (version_compare(PHP_VERSION, '5.0.0', '>=')) {
    // PHP 5 code here
} else {
    // PHP 4 code here
}

Keywords

PHP 4 PHP 5 backward compatibility version checking compatibility testing

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