files and directories - What is the difference between a .wl package and a .m package?

In Mathematica 10.x, one now has both .wl Wolfram Language Packages and .m Wolfram Mathematica Packages.

• What's the difference?


• Is one of the two formats to be preferred in certain situations and, if so, which one and where?


• Why, after making the menu selection File > New > Package, entering code, and saving, is it offered as default to save in the .wl format?

I have read the discussion here, but failed to see there satisfactory answers to those questions.

Note: I don't find any listing of Wolfram Language Package here.