1 files changed, 40 insertions, 1 deletions
diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
index 4412377fa3..c2a5e42914 100644
--- a/Documentation/technical/api-parse-options.txt
+++ b/Documentation/technical/api-parse-options.txt
@@ -8,7 +8,8 @@ Basics
 ------
 
 The argument vector `argv[]` may usually contain mandatory or optional
-'non-option arguments', e.g. a filename or a branch, and 'options'.
+'non-option arguments', e.g. a filename or a branch, 'options', and
+'subcommands'.
 Options are optional arguments that start with a dash and
 that allow to change the behavior of a command.
 
@@ -48,6 +49,33 @@ The parse-options API allows:
   option, e.g. `-a -b --option -- --this-is-a-file` indicates that
   `--this-is-a-file` must not be processed as an option.
 
+Subcommands are special in a couple of ways:
+
+* Subcommands only have long form, and they have no double dash prefix, no
+  negated form, and no description, and they don't take any arguments, and
+  can't be abbreviated.
+
+* There must be exactly one subcommand among the arguments, or zero if the
+  command has a default operation mode.
+
+* All arguments following the subcommand are considered to be arguments of
+  the subcommand, and, conversely, arguments meant for the subcommand may
+  not preceed the subcommand.
+
+Therefore, if the options array contains at least one subcommand and
+`parse_options()` encounters the first dashless argument, it will either:
+
+* stop and return, if that dashless argument is a known subcommand, setting
+  `value` to the function pointer associated with that subcommand, storing
+  the name of the subcommand in argv[0], and leaving the rest of the
+  arguments unprocessed, or
+
+* stop and return, if it was invoked with the `PARSE_OPT_SUBCOMMAND_OPTIONAL`
+  flag and that dashless argument doesn't match any subcommands, leaving
+  `value` unchanged and the rest of the arguments unprocessed, or
+
+* show error and usage, and abort.
+
 Steps to parse options
 ----------------------
 
@@ -110,6 +138,13 @@ Flags are the bitwise-or of:
 	turns it off and allows one to add custom handlers for these
 	options, or to just leave them unknown.
 
+`PARSE_OPT_SUBCOMMAND_OPTIONAL`::
+	Don't error out when no subcommand is specified.
+
+Note that `PARSE_OPT_STOP_AT_NON_OPTION` is incompatible with subcommands;
+while `PARSE_OPT_KEEP_DASHDASH` and `PARSE_OPT_KEEP_UNKNOWN_OPT` can only be
+used with subcommands when combined with `PARSE_OPT_SUBCOMMAND_OPTIONAL`.
+
 Data Structure
 --------------
 
@@ -241,7 +276,11 @@ There are some macros to easily define options:
 	can be given by the user. `int_var` is set to `enum_val` when the
 	option is used, but an error is reported if other "operating mode"
 	option has already set its value to the same `int_var`.
+	In new commands consider using subcommands instead.
 
+`OPT_SUBCOMMAND(long, &fn_ptr, subcommand_fn)`::
+	Define a subcommand.  `subcommand_fn` is put into `fn_ptr` when
+	this subcommand is used.
 
 The last element of the array must be `OPT_END()`.