During my research on what's the difference between match_parent and fill_parent, I found that at the time of API 8 epoch Google just 'renamed' fill_parent to match_parent since the latter better describes the effect and made fill_parent deprecated.
What is silly to me, being official and solid IDE at least in code inspection part, after so many years Android Studio 2.3.3 still doesn't highlight usages of fill_parent as deprecated and not asking to change it to match_parent. It doesn't strike fill_parent through  in suggestion lists also.
So the question is should we ALWAYS use match_parent instead of fill_parent in  new code or using them interchangeably  is kind of established practice in Android development and this is the reason why Android Studio doesn't warn us about the deprecation of fill_parent?