insert the contents of a register by typing `{register}`
Problems:
* If the text in register 0 contains any characters that have special meaning within the replacement field (such as & or ~, for example), we would have to edit the string by hand to escape those characters.
* If register 0 contained a multiline excerpt of text, it might not fit on the command line.
Pass by Reference
`\=`: evaluate a Vim script expression.
`@{register}`: reference the contents of a register (`@0` returns the contents of the yank register, while `@"` returns the contents of the default register.)
Comparison
Example:
equivalent to:
`:let @/='Pragmatic Vim'`: sets the search pattern
* equivalent to: `/Pragmatic Vim `
* does not create a record in the search history
`:let @a='Practical Vim'`: sets the contents of the `a` register
* equivalent to: visually selected the text "Practical Vim" and then typed `"ay` to yank the selection into register `a`.