registers - a
Registers are named lists of text -instead of simply text- in order to interact well with multiselection. They are used for various purposes, like storing the last yanked text, or the captured groups associated with the selections.
non alphanumeric registers have an alternative name that can be used in contexts where only alphanumeric identifiers are possible.
Most commands using a register default to a specific one if not specified:
Some registers are not general purposes, they cannot be written to, but they contain some special data
Registers 1 to 9 hold the grouped sub-matches of the regular expression used to make the last selection. Example: applying the following regular expression to the date of the day would put the day of the week in register 1, the month in register 2, and the day of the month in register 3, but select the entire date:
(\w+) (\w+) (\d+) .+