I found some code on the web to implement multi-step forms in Drupal 7, and currently dissecting it and trying to understand it. (My PHP understanding is decent, but not "great.") I've got most of it worked out and understood, and now I'm flipping the code to put into a multi-step user registration form. So I print out the $form array on the user registration form, and here's a snippet of what I get (edited down for simplicity).
Array
(
[account] => Array
(
[name] => Array
(
[#type] => textfield
[#title] => Username
[#maxlength] => 60
[#description] => Spaces are allowed; punctuation is not allowed except for periods....
)
[mail] => Array
(
[#type] => textfield
[#title] => E-mail address
[#description] => A valid e-mail address. All e-mails from the system...
)
)
)
Now here's a snippet of my code for my custom module...
static $steps = array(
'account' => -1,
);
return $steps;
In a nutshell, this code targets and manipulates everything in the [account] array, and it works.