inspect-register-assignment.md

Download the inspect-registers.vim file from this gist. Open the file in Vim, launching with no vimrc:

vim -Nu NONE inspect-registers.vim

Source the file:

:source %

Insert text on line one:

:0put='Word by word, line by line'

Then run :w to save the buffer.

Execute operations and inspect registers

for {OPERATION} in [yw, yy, "ayw, "ayy, dw, dd, "adw, "add]

1. QQ to clear the registers
2. gg to place the cursor at the start of line one
3. {OPERATION}
4. QW to inspect the registers
5. :e! to revert any changes to the document

Results

When {OPERATION} is yw:

:RegInspect
--- Registers ---
""   Word
"0   Word
"1
"a
"-

When {OPERATION} is yy:

:RegInspect
--- Registers ---
""   Word by word, line by line^J
"0   Word by word, line by line^J
"1
"a
"-

When {OPERATION} is "ayw:

:RegInspect
--- Registers ---
""   Word
"0
"1
"a   Word
"-

When {OPERATION} is "ayy:

:RegInspect
--- Registers ---
""   Word by word, line by line^J
"0
"1
"a   Word by word, line by line^J
"-

When {OPERATION} is dw:

:RegInspect
--- Registers ---
""   Word
"0
"1
"a
"-   Word

When {OPERATION} is dd:

:RegInspect
--- Registers ---
""   Word by word, line by line^J
"0
"1   Word by word, line by line^J
"a
"-

When {OPERATION} is "adw:

:RegInspect
--- Registers ---
""   Word
"0
"1   Word
"a   Word
"-

When {OPERATION} is "add:

:RegInspect
--- Registers ---
""   Word by word, line by line^J
"0
"1   Word by word, line by line^J
"a   Word by word, line by line^J
"-

Summary

This table summarizes the results:

{OPERATION}	"" (default)	"0 (yank)	"1 (numbered)	"a (named)	"- (small delete)
yw	X	X	-	-	-
yy	X	X	-	-	-
"ayw	X	-	-	X	-
"ayy	X	-	-	X	-
dw	X	-	-	-	X
dd	X	-	X	-	-
"adw	X	-	X	X	-
"add	X	-	X	X	-

inspect-registers.vim

command! RegClear :let @a='' | let @-='' | let @0='' | let @1=''
command! RegInspect :reg "a-01
nnoremap QQ :RegClear<CR>
nnoremap QW :RegInspect<CR>

I never realized it was possible to Gist a markdown file and have it rendered nicely.
The register info is great, too.