The php checkdate function checkdate() checks the validity of the date passed as arguments of month, day and year, it return TRUE if the given date is valid, otherwise returns FALSE

The php chdir() function changes PHP’s current directory to another directory passed as a string parameter called ‘$directory’

The php base_convert() function is used convert numbers between arbitrary bases, for example you can convert a decimal number to binary or Hex. Definition: string base_convert ( string $number , int $frombase , int $tobase ) Example: $d=’3′; $hex=’A37334′; echo base_convert($d , 10 , 2); echo ‘<br/>’; echo base_convert($hex , 16 , 2); Output: 11 [...]

The php base64_encode function is used to encodes data with MIME base64 to transport data through layers that are not 8-bit clean, after encoding the result will take 33% more space than the original data.

php base64_decode function is used to decode the given data  encoded with MIME base64, it returns FALSE if the input data contains character from outside the base64 alphabet.

The php assert_options function is used to set or read the various assert flags, below there is a list of some values that can be used

The php function assert() is a build in function that will check the given assertion parameter and take correct action if its result is FALSE. the assertion is given as a string that will be evaluated as PHP code.