Crash course on adding custom field to mod search

Hi Guys,

I have looked into the view.html of users, its method search and the template of the mod search. I'm aware that the mod push 4 array: conditions, criteria, datakeys & operators.

Operators is pretty straightforward... however could you provide the full list. (A)
Conditions seems to push the field value to analyse against.

I'm less sure about how criteria and datakeys are working... especially since I'm not aware how the method, and it's option ($model->getUsersByFilter('0', $options, $searchOptions) are really working. (B)

I will want to had a select field (or select2 whatsoever) to check against a custom field in one's profile. Like Profession with a lot of profession.

Not sure about the CLEAN UP loop (C) ... which seems a clean up method for complex condition... and the searchOption if-statement (D)

A little crash course would be welcome, in general, and on A, B, C & D above, which I'm sure could become a future page of your I-HOPE-SOON-TO-BE documentation

Thanks Guys,

EDIT... : and why the criterias is XXXXXX/xxxxxxx

[criterias] => Array
(
[0] => JOOMLA_FULLNAME|joomla_fullname
[1] => GENDER|gender
)