Colon use inside function declaration

Question

I saw a code, where a colon was used inside a function declaration:

DoWork(Param1:Param2)

I know that a colon is for inheritance: class Child: Parent But, what is the purpose of the colon when it used before variable?

EDIT I've corrected the question

Answer 1

Named optional arguments

Its so you can have an optional number of arguments supplied, but the compiler needs to know which arguments to marry up to which parameters, otherwise defaults will be used for the others.