Difference between the ".wl" and the ".m" file types?

Questions
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1

In Mathematica 10.3.1.0, the File, New, Package menu item creates “.wl” files. The documentation for “Setting Up Wolfram Language Package” (tutorial/SettingUpWolframLanguagePackages) makes reference to “.m” files.

What is the difference between the “.wl” and the “.m” file types?

When should each one be used?

2

Please see my post with the same questions, and some others’ comments on it, at:

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

3

I think they are pretty much the same. Possibly new .wl extension is to help promote Wolfram Language and set aside from other companies .m formats. Some of the comments @Murray Eisenberg linked to go along same lines.