multi-dimensional array:

$table = array(

    1 => array(1 => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12),

    2 => array(1 => 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24),

    3 => array(1 => 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36),

... 

);

PHP validation is done by regex?

custom error handling, why isn't this made more use of?

oooooh! libraries for authoring pdfs?.....reading the internet...

md5()