haXe defines some types that may already exist in the target platform.
For example, haXe defines the Array class. The Array class is already defined on almost all target platforms. The thing is that on some targets, the haXe array and the native array may indeed be different.
In such cases, when working with externs, you may need to convert from a haXe array to a native array and vice-versa.
You have to pay particular attention to that when working with Neko and PHP.
If you are targeting Neko or PHP, then you will have to pay particular attention to array and string. Indeed, in the Neko and PHP packages, you will find the native array and native string types.
There are also 'functions and methods that you can use to convert a native type to the haXe one.