Why doesn't emmet in Atom expand standard html markup?

Question

HTML

Good afternoon!
I recently installed Atom and tried to finish a project I had already started and found that emmet worked. This pleasantly surprised me. But now I started writing a new project, and introduced the habits of "!" and pressed tab but nothing worked. Standard markup did not appear. But at the same time, the rest of the functionality of emmet works. How to fix this problem?

Answer 1

Are there emmet in "Packages"?
Is the file extension exactly .html/.htm?