ne's manual

4.5.9: CaseSearch

distinguish between the upper case and lower case versions of a letter. By default the flag is false, since this seems to be what most user want.

If you call this command with no arguments, it will toggle the flag. If you specify 0 or 1, the flag will be set to false or true, respectively. A lower case `c' will appear on the status bar if the flag is true.