--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/help/revisions.txt	Sun Oct 04 09:59:13 2009 +0200
@@ -0,0 +1,29 @@
+    Mercurial supports several ways to specify individual revisions.
+
+    A plain integer is treated as a revision number. Negative integers
+    are treated as sequential offsets from the tip, with -1 denoting
+    the tip, -2 denoting the revision prior to the tip, and so forth.
+
+    A 40-digit hexadecimal string is treated as a unique revision
+    identifier.
+
+    A hexadecimal string less than 40 characters long is treated as a
+    unique revision identifier and is referred to as a short-form
+    identifier. A short-form identifier is only valid if it is the
+    prefix of exactly one full-length identifier.
+
+    Any other string is treated as a tag or branch name. A tag name is
+    a symbolic name associated with a revision identifier. A branch
+    name denotes the tipmost revision of that branch. Tag and branch
+    names must not contain the ":" character.
+
+    The reserved name "tip" is a special tag that always identifies
+    the most recent revision.
+
+    The reserved name "null" indicates the null revision. This is the
+    revision of an empty repository, and the parent of revision 0.
+
+    The reserved name "." indicates the working directory parent. If
+    no working directory is checked out, it is equivalent to null. If
+    an uncommitted merge is in progress, "." is the revision of the
+    first parent.