The -, _, and leading _ are just variations of white space / separator I have encountered. I think it's possible to document all the allowable values in the Javadoc section of the function that takes in string as their argument.
In the specific android example, I would put it here.
Under projection params where it takes in all the Images.Media.* string consts.
In the specific android example, I would put it here. Under projection params where it takes in all the Images.Media.* string consts.
https://developer.android.com/reference/android/content/Cont...
Though, if it's a practice of Java Engineer to document allowable enum like string as a constant, then I can say that's a valid argument.