Used mainly in instant messaging programs and emails.
Used with words that have the same letter in the middle which could mean two different things according the number of that letter in the middle of that word.
Roy: Wwwttff??!!? ddiidd Iii see thaat awweessoomee carrtoonn, off liikee miillkkk? I'mmm coonffuusseed...
Dave: Heyyy, I'lll prelongate itt foorr yoouuu: "Did you see that awesome cartoon?"
Roy: Oooohh rrigghhtt yyeeaahh itt wass bittchhiiinn, tthhee bitt whheeree thhee maaiinn chharractterr aattee thhat dooggss taaill Iiii LOLZOOORRREEDD!