[TYPO3-english] question about coding in MTB23

[tom]

Hi,

Below code is from MTB23(Modern Template Building, Part 2+3),
\typo3conf\ext\tmplselect\class.tx_tmplselect_addfilestosel.php

class tx_tmplselect_addfilestosel {
 var $dir = "main";

 function main(&$params,&$pObj) {
   // Adding an item!
  $params["items"][]=Array($pObj->sL("Mode: ".$this->dir), 999);
 }
}
...

My questions are:

1. $params,what does this mean? or how does this work? from
'$params["items"][]...', I just know it is an arrar.

2. $pObj, what does this mean?

3. Array($pObj->sL("Mode: ".$this->dir), 999);'->sL', is sL a method?
where can I check the usage of sL? what does '999' mean?

Thanks.



Tom