[SugarCube 2] Array Functions

Hi, time for another newbie question.

Is there a document or webpage the defines array functions in Twine 2/Sugar Cube 2?
I've gotten examples of $array.push() and $array.pop() and $array.length that aren't listed on the SugarCube website motoslave.net/sugarcube/2/#documentation. And now I'm looking for some more obscure array functions that I remember using from other programming languages. Example:

I need a function like $array.position("X") that would return the position index of the value "X" from an array.

Are these array functions from SugarCube or Twine? Are they javascript? HTML? or something else? And where can I find a document defining them?

Thanks.