qlik sense expression

[safae11]

can any one explain to me what these  lines gives as output 

ps: all parameter  are date format

if(len(trim([T3 Contingenté]))>0,

      //"T3 Date Révisée Validée" - "T3 Contingenté",

     if(len(trim([T3 Date Réelle]))>0,

     "T3 Date Réelle" - "T3 Contingenté",

      Today() - "T3 Contingenté"),

     0 )

[vinieme12]

No of days between the dates