Apex outputtext value attribute

 Here, 0 tells you which argument index to merge in. So usually, you just have one argument, and merging it in uses the 0-index parameter. But you might for some reason have multiple arguments (each represented by an ). As represented by the above example, you can merge multiple arguments into one format string. It is very similar behavior to the String.format method in Apex, though I don't believe you can do date formatting that way.