Netbeans uses fake php files called 'stubs' that can be included in your project (just let them sit somewhere in a place that netbeans scans.
Example for built in php functions: (See NetbeansFolder/php/phpstubs, or ctrl-click in netbeans on a native php function).
/**
* (PHP 4 >= 4.2.0, PHP 5)<br/>
* Changes all keys in an array
* @link http://php.net/manual/en/function.array-change-key-case.php
* @param array $input <p>
* The array to work on
* </p>
* @param int $case [optional] <p>
* Either <b>CASE_UPPER</b> or
* <b>CASE_LOWER</b> (default)
* </p>
* @return array an array with its keys lower or uppercased, or false if
* <i>input</i> is not an array.
*/
function array_change_key_case (array $input, $case = 'CASE_LOWER') {}