Index: head/tools/build/options/WITH_DIRDEPS_BUILD
===================================================================
--- head/tools/build/options/WITH_DIRDEPS_BUILD	(revision 298006)
+++ head/tools/build/options/WITH_DIRDEPS_BUILD	(revision 298007)
@@ -1,39 +1,35 @@
 .\" $FreeBSD$
-Enable building in meta mode.
-This is an experimental build feature.
+This is an experimental build system.
 For details see
 http://www.crufty.net/sjg/docs/freebsd-meta-mode.htm.
-.Pp
+Build commands can be seen from the top-level with:
+.Dl make show-valid-targets
 The build is driven by dirdeps.mk using
 .Va DIRDEPS
 stored in
 Makefile.depend files found in each directory.
 .Pp
 The build can be started from anywhere, and behaves the same.
 The initial instance of
 .Xr make 1 
 recursively reads
 .Va DIRDEPS
 from Makefile.depend
 computing a graph of tree dependencies from the current origin.
 Setting
 .Va NO_DIRDEPS
 will skip checking dirdep dependencies and will only build in the current
 and child directories.
 .Va NO_DIRDEPS_BELOW
 will skip building any dirdeps and only build the current directory.
 .Pp
-As each target is made
-.Xr make 1
-produces a meta file which is used to capture (and compare)
-the command line,
-as well as any command output.
-If
-.Xr filemon 4
-is available the meta file will also capture a record of files
-used to produce the target by tracking syscalls.
+This also utilizes the
+.Va WITH_META_MODE
+logic for incremental builds.
 .Pp
 The build will hide commands ran unless
 .Va NO_SILENT
 is defined.
+.Pp
+Note that there is currently no mass install feature for this.
 .Pp
Index: head/tools/build/options/WITH_META_MODE
===================================================================
--- head/tools/build/options/WITH_META_MODE	(revision 298006)
+++ head/tools/build/options/WITH_META_MODE	(revision 298007)
@@ -1,12 +1,41 @@
 .\" $FreeBSD$
-Create meta files when not doing DIRDEPS_BUILD.
+Creates
+.Xr make 1
+meta files when building, which can provide a reliable incremental build when
+using
+.Xr filemon 4 .
+The meta file is created in the OBJDIR as
+.Pa target.meta .
+These meta files track the command ran, its output, and the current directory.
 When the
 .Xr filemon 4
-module is loaded, dependencies will be tracked for all commands.
-If any command, its dependencies, or files it generates are missing then
-the target will be considered out-of-date and rebuilt.
+module is loaded, any files used by the commands executed will be tracked as
+dependencies for the target in its meta file.
+The target will be considered out-of-date and rebuilt if any of the following
+are true compared to the last build:
+.Bl -bullet -compact
+.It
+The command to execute changes.
+.It
+The current working directory changes.
+.It
+The target's meta file is missing.
+.It
+[requires
+.Xr filemon 4 ]
+Files read, executed or linked to are newer than the target.
+.It
+[requires
+.Xr filemon 4 ]
+Files read, written, executed or linked are missing.
+.El
 The meta files can also be useful for debugging.
 .Pp
 The build will hide commands ran unless
 .Va NO_SILENT
 is defined.
+.Pp
+The build operates as it normally would otherwise.
+This option originally invoked a different build system but that was renamed
+to
+.Va WITH_DIRDEPS_BUILD .