MillScript unifies the common syntaxes for function calls and methods calls. The best way to understand this is to see that there is one general form and two simplified versions.
x.f( y, z ) # general form
f( x, y, z ) # prefix variant
x.f # variant, best used with single argument
The general form allows you to put the first argument on the left hand side of the function - the remainder being bracketed on the right hand side. However, one may omit the left hand argument or the right hand arguments (not both!) to create the two simplified variants.
It is purely a matter of style which of the three variants you choose
to use. I suggest the following guideline. When you wish to focus the
reader's attention on the first argument, use the general form. It
suggests that the function is principally acting on that argument and
the other arguments are subsidary in their role. The prefix variant is
suitable when all arguments are of equal relevance. The postfix
variant is only really appropriate when there is a single argument. It
works nicely when you are composing sequences of function applications
e.g. x.foo.bar.gort. Another good use is for accessing
fields of data structures i.e. instance variables.