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If your wondering what SEF stands for it is an SEO function for URL generation that stands for 'Search Engine Friendly'!
Preloaders should not really be thought about as a 'cron' this is what is called a hooking stratum, which is how Microsoft windows events and processings works unlike linux. This is where is was adopted from.
This file is normally called sef.php in the modules/dirname/preloaders path from memory... it will load a css style sheet from modules/language/dirname as dirname.css in modules.