Optional arguments vs default values

I find the pages on [optional arguments](https://haxe.org/manual/types-function-optional-arguments.html) and [default values](https://haxe.org/manual/types-function-default-values.html) a bit confusing. They fail to mention that optional arguments are just syntactic sugar for a default value of `null` / that `?param:SomeType` is the same as `param:Null = null`. To somebody that doesn't know that, it can read like optional arguments and default values are entirely different things.