Type: format string
Default: "%u%D%t%2n %T%.40d%> [%.7m/%.10M, %.6e, %s] "
This variable describes the format of the `attachment' menu. The following printf-style sequences are understood:
%D deleted flag
%d description
%e MIME content-transfer-encoding
%f filename
%m major MIME type
%M MIME subtype
%n attachment number
%s size
%t tagged flag
%u unlink (=to delete) flag
%>X right justify the rest of the string and pad with character "X"
%|X pad to the end of the line with character "X"