How does the InsertChange event work?

Question

So this is in the help page (:h autocmd-events):

|InsertChange|      when typing <Insert> while in Insert or Replace mode

I don't really understand what it means with when typing <Insert>. So I tried it out by adding this into my init.vim file:

autocmd InsertChange <buffer> echo "yes"

then I opened a file and typed some random characters but yes isn't printed out. How is it suppose to work?

EDIT I also looked into the more detailed description of InsertChange:

                            *InsertChange*
InsertChange            When typing <Insert> while in Insert or
                Replace mode.  The |v:insertmode| variable
                indicates the new mode.
                Be careful not to move the cursor or do
                anything else that the user does not expect.

But I still don't understand what <Insert> is supposed to be.

Answer 1

InsertChange is called when the type of insert mode changes; that is, if you change from insert to replace mode by pressing the Insert key.

With this:

autocmd InsertChange * :echom 'change to: ' . v:insertmode

Pressing i<Insert><Insert> should give you:

change to: r
change to: i

There is also a "visual replace" mode (which I just learned about!), and pressing gR<Insert><Insert>:

change to: i
change to: v

These are the only cases where this autocmd is triggered, in the ins_insert() function in edit.c