Please use php tags around the code, it's hard to read as you wrote it. You should do it if you need in your plugin.
Not a fixed usage.
It's the same as swapping two variables values
PHP Code:
new var = 5
new var2 = 6
new aux
aux = var
var = var2
var2 = aux
//Now var is 6 and var 2 is 5
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