New -boot_image setting mbr_force_bootable=, -as mkisofs --mbr-force-bootable

xorriso/xorriso.texi

@@ -50,7 +50,7 @@
 @c man .\" First parameter, NAME, should be all caps
 @c man .\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
 @c man .\" other parameters are allowed: see man(7), man(1)
-@c man .TH XORRISO 1 "Version 1.4.3, Dec 08, 2015"
+@c man .TH XORRISO 1 "Version 1.4.3, Dec 30, 2015"
 @c man .\" Please adjust this date whenever revising the manpage.
 @c man .\"
 @c man .\" Some roff macros, for reference:
@@ -3946,6 +3946,16 @@ to an aligned size.
 @*
 Mode "off" disables alignment for any type.
 @*
+@cindex MBR bootable/active flag, enforce
+@strong{mbr_force_bootable=}mode enforces an MBR partition with
+"bootable/active" flag if options like partition_table= or grub2_mbr=
+indicate production of a bootable MBR.
+These options normally cause the flag to be set if there is an
+MBR partition of type other than 0xee or 0xef.
+If no such partition exists, then no bootflag is set, unless
+mbr_force_bootable= forces creation of a dummy partition
+of type 0x00 which covers only the first block of the ISO image.
+@*
 @cindex MIPS boot file, activation
 @strong{mips_path=}iso_rr_path declares a data file in the image to be a
 MIPS Big Endian boot file and causes production of a MIPS Big Endian Volume