diff --git a/docs/manifest-format.txt b/docs/manifest-format.txt
index a7bb156..e5f5ee1 100644
--- a/docs/manifest-format.txt
+++ b/docs/manifest-format.txt
@@ -43,12 +43,17 @@
     <!ELEMENT manifest-server (EMPTY)>
     <!ATTLIST url              CDATA #REQUIRED>
   
-    <!ELEMENT project (EMPTY)>
+    <!ELEMENT project (annotation?)>
     <!ATTLIST project name     CDATA #REQUIRED>
     <!ATTLIST project path     CDATA #IMPLIED>
     <!ATTLIST project remote   IDREF #IMPLIED>
     <!ATTLIST project revision CDATA #IMPLIED>
     <!ATTLIST project groups   CDATA #IMPLIED>
+
+    <!ELEMENT annotation (EMPTY)>
+    <!ATTLIST annotation name  CDATA #REQUIRED>
+    <!ATTLIST annotation value CDATA #REQUIRED>
+    <!ATTLIST annotation keep  CDATA "true">
   
     <!ELEMENT remove-project (EMPTY)>
     <!ATTLIST remove-project name  CDATA #REQUIRED>
@@ -163,6 +168,17 @@
 whitespace or comma separated.  All projects are part of the group
 "default" unless "-default" is specified in the list of groups.
 
+Element annotation
+------------------
+
+Zero or more annotation elements may be specified as children of a
+project element. Each element describes a name-value pair that will be
+exported into each project's environment during a 'forall' command,
+prefixed with REPO__.  In addition, there is an optional attribute
+"keep" which accepts the case insensitive values "true" (default) or
+"false".  This attribute determines whether or not the annotation will
+be kept when exported with the manifest subcommand.
+
 Element remove-project
 ----------------------
 
diff --git a/manifest_xml.py b/manifest_xml.py
index a250382..9b804da 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -203,6 +203,13 @@
       if p.groups:
         e.setAttribute('groups', ','.join(p.groups))
 
+      for a in p.annotations:
+        if a.keep == "true":
+          ae = doc.createElement('annotation')
+          ae.setAttribute('name', a.name)
+          ae.setAttribute('value', a.value)
+          e.appendChild(ae)
+
     if self._repo_hooks_project:
       root.appendChild(doc.createTextNode(''))
       e = doc.createElement('repo-hooks')
@@ -545,6 +552,8 @@
     for n in node.childNodes:
       if n.nodeName == 'copyfile':
         self._ParseCopyFile(project, n)
+      if n.nodeName == 'annotation':
+        self._ParseAnnotation(project, n)
 
     return project
 
@@ -556,6 +565,17 @@
       # dest is relative to the top of the tree
       project.AddCopyFile(src, dest, os.path.join(self.topdir, dest))
 
+  def _ParseAnnotation(self, project, node):
+    name = self._reqatt(node, 'name')
+    value = self._reqatt(node, 'value')
+    try:
+      keep = self._reqatt(node, 'keep').lower()
+    except ManifestParseError:
+      keep = "true"
+    if keep != "true" and keep != "false":
+      raise ManifestParseError, "optional \"keep\" attribute must be \"true\" or \"false\""
+    project.AddAnnotation(name, value, keep)
+
   def _get_remote(self, node):
     name = node.getAttribute('remote')
     if not name:
diff --git a/project.py b/project.py
index 49fef2f..e297926 100644
--- a/project.py
+++ b/project.py
@@ -213,6 +213,11 @@
     Coloring.__init__(self, config, 'diff')
     self.project   = self.printer('header',    attr = 'bold')
 
+class _Annotation:
+  def __init__(self, name, value, keep):
+    self.name = name
+    self.value = value
+    self.keep = keep
 
 class _CopyFile:
   def __init__(self, src, dest, abssrc, absdest):
@@ -529,6 +534,7 @@
 
     self.snapshots = {}
     self.copyfiles = []
+    self.annotations = []
     self.config = GitConfig.ForRepository(
                     gitdir = self.gitdir,
                     defaults =  self.manifest.globalConfig)
@@ -1175,6 +1181,9 @@
     abssrc = os.path.join(self.worktree, src)
     self.copyfiles.append(_CopyFile(src, dest, abssrc, absdest))
 
+  def AddAnnotation(self, name, value, keep):
+    self.annotations.append(_Annotation(name, value, keep))
+
   def DownloadPatchSet(self, change_id, patch_id):
     """Download a single patch set of a single change to FETCH_HEAD.
     """
diff --git a/subcmds/forall.py b/subcmds/forall.py
index d3e70ae..9436f4e 100644
--- a/subcmds/forall.py
+++ b/subcmds/forall.py
@@ -82,6 +82,11 @@
 REPO_RREV is the name of the revision from the manifest, exactly
 as written in the manifest.
 
+REPO__* are any extra environment variables, specified by the
+"annotation" element under any project element.  This can be useful
+for differentiating trees based on user-specific criteria, or simply
+annotating tree details.
+
 shell positional arguments ($1, $2, .., $#) are set to any arguments
 following <command>.
 
@@ -162,6 +167,8 @@
       setenv('REPO_REMOTE', project.remote.name)
       setenv('REPO_LREV', project.GetRevisionId())
       setenv('REPO_RREV', project.revisionExpr)
+      for a in project.annotations:
+        setenv("REPO__%s" % (a.name), a.value)
 
       if mirror:
         setenv('GIT_DIR', project.gitdir)