mercurial/help/revisions.txt

wireproto: unescape argument names in batch command (BC)

Clients escape both argument names and values when using the
batch command. Yet the server was only unescaping argument values.

Fortunately we don't have any argument names that need escaped. But
that isn't an excuse to lack symmetry in the code.

Since the server wasn't properly unescaping argument names, this
means we can never introduce an argument to a batchable command that
needs escaped because an old server wouldn't properly decode its name.
So we've introduced an assertion to detect the accidental introduction
of this in the future. Of course, we could introduce a server
capability that says the server knows how to decode argument names and
allow special argument names to go through. But until there is a need
for it (which I doubt there will be), we shouldn't bother with adding
an unused capability.

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.