mercurial/help/revisions.txt

help: branch names primarily denote the tipmost unclosed branch head

Was the behavior correct and the description wrong so it should be updated as
in this patch? Or should the code work as the documentation says?

Both ways could make some sense ... but none of them are obvious in all cases.

One place where it currently cause problems is when the current revision has
another branch head that is closer to tip but closed. 'hg rebase' refuses to
rebase to that as it only see the tip-most unclosed branch head which is the
current revision.

/me kind of likes named branches, but no so much how branch closing works ...

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 bookmark, tag, or branch name. A
bookmark is a movable pointer to a revision. A tag is a permanent name
associated with a revision. A branch name denotes the tipmost open branch head
of that branch - or if they are all closed, the tipmost closed head of the
branch. Bookmark, tag, and branch names must not contain the ":" character.

The reserved name "tip" 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.