What is the ‘bomb’ option?

When reading a file with “ucs-bom” present in the ‘fileencodings’ option, Vim will set the ‘bomb’ option on or off depending on the presence or absence of a byte-order mark at the start of the file. When writing, Vim will write a byte-order mark if the ‘bomb’ option is set. You may set or unset it manually do make Vim write, or not write, the b.o.m.