Is there a standard to interpret the syntax of function interfaces in API documentations and if yes, how is it defined?

Here is an example on how to change the color of an item the JavaScript scripting guide for Photoshop for the "fillColor" function:

fillPath
([fillColor]
[, mode]
[, opacity]
[, preserveTransparency] [, feather]
[, wholePath] [, antiAlias])

What is the meaning of the brackets and why are there commas in the brackets? How does this relate to the following example calls?

myPath.fillPath(myNewColor)

myPath.fillPath(mynewColor, {
    mode: RGB,
    opacity: .5
})