.base64 "string"[, …]Allows binary data to be entered into a section encoded as a base64 string.
There is no maximum length to the strings, but they must be a multiple of four
bytes long. If necessary the ends of the strings can be padded with =
characters. Line breaks, control characters and escaped characters are not
allowed in the strings. The strings must be enclosed between double quote
characters. Multiple strings are allowed, but they must be separated by
commas.
As an example of how to create a base64 encoded string, see the
base64 program (with its -w0 option to disable line breaks).
Note: for targets where the size of a byte is larger than the size of an octet
the .base64 directive will, if necessary, pad the end of the last
string so that the total number of octets generated are a multiple the number
of octets in a byte.