--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -10,7 +10,7 @@ from node import *
 from i18n import gettext as _
 demandload(globals(), "bisect os re sys signal imp urllib pdb shlex stat")
 demandload(globals(), "fancyopts ui hg util lock revlog bundlerepo")
-demandload(globals(), "difflib patch time")
+demandload(globals(), "difflib patch time help")
 demandload(globals(), "traceback errno version atexit")
 demandload(globals(), "archival changegroup cmdutil hgweb.server sshserver")
 
@@ -1141,6 +1141,24 @@ def help_(ui, name=None, with_version=Fa
             else:
                 ui.write(' %-*s   %s\n' % (m, f, h[f]))
 
+    def helptopic(name):
+        v = None
+        for i in help.helptable:
+            l = i.split('|')
+            if name in l:
+                v = i
+                header = l[-1]
+        if not v:
+            raise UnknownCommand(name)
+
+        # description
+        doc = help.helptable[v]
+        if not doc:
+            doc = _("(No help text available)")
+
+        ui.write("%s\n" % header)
+        ui.write("%s\n" % doc.rstrip())
+
     def helpext(name):
         try:
             mod = findext(name)
@@ -1163,10 +1181,16 @@ def help_(ui, name=None, with_version=Fa
         helplist(modcmds.has_key)
 
     if name and name != 'shortlist':
-        try:
-            helpcmd(name)
-        except UnknownCommand:
-            helpext(name)
+        i = None
+        for f in (helpcmd, helptopic, helpext):
+            try:
+                f(name)
+                i = None
+                break
+            except UnknownCommand, inst:
+                i = inst
+        if i:
+            raise i
 
     else:
         # program name

new file mode 100644
--- /dev/null
+++ b/mercurial/help.py
@@ -0,0 +1,45 @@
+# help.py - help data for mercurial
+#
+# Copyright 2006 Matt Mackall <mpm@selenic.com>
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+helptable = {
+    "dates|Date Formats":
+    r'''
+    Some commands (backout, commit, tag) allow the user to specify a date.
+    Possible formats for dates are:
+
+YYYY-mm-dd \HH:MM[:SS] [(+|-)NNNN]::
+    This is a subset of ISO 8601, allowing just the recommended notations
+    for date and time. The last part represents the timezone; if omitted,
+    local time is assumed. Examples:
+
+    "2005-08-22 03:27 -0700"
+
+    "2006-04-19 21:39:51"
+
+aaa bbb dd HH:MM:SS YYYY [(+|-)NNNN]::
+    This is the date format used by the C library. Here, aaa stands for
+    abbreviated weekday name and bbb for abbreviated month name. The last
+    part represents the timezone; if omitted, local time is assumed.
+    Examples:
+
+    "Mon Aug 22 03:27:00 2005 -0700"
+
+    "Wed Apr 19 21:39:51 2006"
+
+unixtime offset::
+    This is the internal representation format for dates. unixtime is
+    the number of seconds since the epoch (1970-01-01 00:00 UTC). offset
+    is the offset of the local timezone, in seconds west of UTC (negative
+    if the timezone is east of UTC).
+    Examples:
+
+    "1124706420 25200" (2005-08-22 03:27:00 -0700)
+
+    "1145475591 -7200" (2006-04-19 21:39:51 +0200)
+    ''',
+}
+