Understanding various ctrl-r variants in vim

Question

I will use ctrl-r quite frequently in insert mode to insert contents of a register, for example, ", %, or any of the [a-z] registers. I've also come across the following in the help:

tag             char                         action in Insert mode   
-----------------------------------------------------------------------
i_CTRL-R        CTRL-R {register}            insert the contents of a register
i_CTRL-R_CTRL-R CTRL-R CTRL-R {register}     insert the contents of a register literally
i_CTRL-R_CTRL-O CTRL-R CTRL- O {register}    insert the contents of a register literally and don't auto-indent
i_CTRL-R_CTRL-P CTRL-R CTRL-P {register}     insert the contents of a register literally and fix indent.

What exactly is the difference between these? For example, for the insert register literally I was thinking that it would convert something like a newline into a control-sequence, so the text:

Hello

There

Would be converted to something like:

Hello^JThere

But that doesn't seem to be the case. Could someone explain the differences between the four ctrl-r options perhaps using an example for how the four would actually produce a different output when pasted into vim?

Answer 1

A good example to illustrate this is by creating a list and inserting it with CTRL-R and CTRL-R CTRL-R.

:let a=[1,2,3,4]

Now if we insert the contents of a using ctrl-r, the list will appear, with one element per line:

1
2
3
4

However, if we insert the contents of a using ctrl-r ctrl-r, we will see the list-separator (NUL) on that line:

1^@2^@3^@4^@

The two other variants, CTRL-R CTRL-O and CTRL-R CTRL-P are the based on the latter, except the former will not auto-indent and the latter will.

In case a more-visual example is helpful: