--- /dev/null
+@node Usage rules
+@unnumbered Usage rules
+
+@itemize
+
+@item Target is the single file.
+Target's result probably won't create file at all.
+
+@item Build rules for the target @file{target} are placed in
+@file{target.do} file.
+
+@item By default @file{.do} file is run as @code{/bin/sh -e} script.
+If @command{redo} is run with an @option{-x} argument, then
+@code{/bin/sh -ex} is used instead.
+
+@item Executable @file{.do} file is run as is, by direct execution.
+
+@item Targets can be placed in other directories, probably with
+relatives paths.
+
+@item Following @file{.do} files are searched for @file{dir/base.a.b} target:
+
+@example
+dir/base.a.b.do
+dir/default.a.b.do
+dir/default.b.do
+dir/default.do
+default.a.b.do
+default.b.do
+default.do
+@end example
+
+and for @file{../a/b/xtarget.y} target:
+
+@example
+./../a/b/xtarget.y.do
+./../a/b/default.y.do
+./../a/b/default.do
+./../a/default.y.do
+./../a/default.do
+./../default.y.do
+./../default.do
+@end example
+
+@item @file{.do} file search goes up to @file{/} by default, but can be
+ limited with either @env{$REDO_TOP_DIR} environment variable, or by
+ having @file{.redo/top} file in it.
+
+@item @file{.do} runs in the same directory where it is placed.
+
+@item @file{.do} runs with the three arguments:
+ @itemize
+ @item @code{$1} -- name of the target.
+ @item @code{$2} -- base name of the target. Equals to @code{$1} if
+ it is not @file{default.*} file. Otherwise it lacks the extension.
+@example
+a.b.c.do -> $2=a.b.c
+default.do -> $2=a.b.c
+default.c.do -> $2=a.b
+default.b.c.do -> $2=a
+@end example
+ @item @code{$3} -- path to the temporary file, that will be renamed
+ to the target itself. It is relative to the file in the target
+ directory.
+ @end itemize
+
+@item @file{.do}'s @code{stdout} is captured and written to the
+ @code{$3} file. You have to produce either @code{stdout} output, or
+ use @code{$3} directly, but not both.
+
+@item If there was no @code{stdout} output and no @code{$3} file is
+ explicitly created, then no output file is created at all. Target
+ does not produce anything, it is "empty".
+
+@item @code{stderr} is not captured at all and can be seen by default.
+
+@item Empty targets are considered always out-of-date.
+
+@item Dependency information is recorded by @command{redo-ifchange}
+ command invocation. It takes list of dependencies (targets), on
+ whose the currently build target is dependant. Current @file{.do}
+ file is implicitly added as a dependency.
+
+@item If no @command{redo-ifchange}'s dependency target exists, then it
+ is build (according to build rules in corresponding @file{.do}). If
+ dependency has not been changed, then it is not rebuilt.
+
+@item Non-existent files dependencies are created with
+ @command{redo-ifcreate} command. If specified dependency target file
+ appears, then current target will be rebuilt. Intermediate higher
+ priority @file{.do} files dependency is implicitly recorded. For
+ example, if you @file{foo} target currently uses @file{default.do}
+ script, then @file{foo.do} is automatically recorded as a
+ non-existent dependency, forcing @file{foo} to be rebuilt if
+ @file{foo.do} appears.
+
+@end itemize