The Read-only Register

Neovim's "read-only" registers are useful for quickly repeating actions or accessing file information.

There are three "read-only" registers, which provide access to the following information:

".
Contains the most-recently inserted text. This is updated each time Vim is in insert mode, and allows (for example) the same text to be pasted into the document multiple times.
"%
Contains the name of the current file, which makes it useful in commands that operate on the entire file.
":
Contains the most recent command that was executed on the command-line. As with the other registers in this section, this can be used to repeat the same multiple times without having to type it in each time.