This defines what bases Vim will consider for numbers when using the CTRL-A and CTRL-X commands for adding to and subtracting from a number respectively; see |CTRL-A| for more info on these commands. alpha If included, single alphabetical characters will be incremented or decremented. This is useful for a list with a letter index a), b), etc. octal If included, numbers that start with a zero will be considered to be octal. Example: Using CTRL-A on "007" results in "010". hex If included, numbers starting with "0x" or "0X" will be considered to be hexadecimal. Example: Using CTRL-X on "0x100" results in "0x0ff". bin If included, numbers starting with "0b" or "0B" will be considered to be binary. Example: Using CTRL-X on "0b1000" subtracts one, resulting in "0b0111". unsigned If included, numbers are recognized as unsigned. Thus a leading dash or negative sign won't be considered as part of the number. Examples: Using CTRL-X on "2020" in "9-2020" results in "9-2019" (without "unsigned" it would become "9-2021"). Using CTRL-A on "2020" in "9-2020" results in "9-2021" (without "unsigned" it would become "9-2019"). Using CTRL-X on "0" or CTRL-A on "18446744073709551615" (2^64 - 1) has no effect, overflow is prevented. Numbers which simply begin with a digit in the range 1-9 are always considered decimal. This also happens for numbers that are not recognized as octal or hex.