Unique identifiers for entries can now be used more efficiently.
Internally, a hash array has replaced the alist used so far to
keep track of the files in which an ID is defined. This makes it
quite fast to find an entry by ID.
There is now a new link type which looks like this:
id:GLOBALLY-UNIQUE-IDENTIFIER
This link points to a specific entry. When you move the entry to
a different file, for example if you move it to an archive
file, this link will continue to work.
The file /org-id.el/ contains an API that can be used to write
code using these identifiers, including creating IDs and finding
them wherever they are.
Org has its own method to create unique identifiers, but if the
system has /uuidgen/ command installed (Mac's and Linux systems
generally do), it will be used by default. You an also select
the method by hand, using the variable =org-id-method=.
If the ID system ever gets confused about where a certain ID is,
it initiates a global scan of all agenda files with associated
archives, all files previously known containing any IDs, and all
currently visited Org-mode files to rebuild the hash. You can
also initiate this by hand: =M-x org-id-update-id-locations=.
Running this command will also dump into the =*Messages*= buffer
information about any duplicate IDs. These should not exist, but
if you /copy/ an entry with its properties, duplicate IDs will
inevitably be produced. This is unavoidable in a plain text
system that allows you to edit the text in arbitrary ways, and a
portion of care on your side is needed to keep this system clean.
The hash is stored in the file =~/.emacs.d/.org-id-locations=.
This is also a change from previous versions where the file was
=~/.org=id-locations=. Therefore, you can remove this old file
if you have it. I am not sure what will happen if the =.emacs.d=
directory does not exists in your setup, but in modern Emacsen, I
believe it should exist. If you do not want to use IDs across
files, you can avoid the overhead with tracking IDs by
customizing the variable =org-id-track-globally=. IDs can then
still be used for links inside a single file.
IDs will also be used when you create a new link to an Org-mode
buffer. If you use =org-store-link= (normally at =C-c l=) inside
en entry in an Org-mode buffer, and ID property will be created
if it does not exist, and the stored link will be an =id:= link.
If you prefer the much less secure linking to headline text, you
can configure the variable =org-link-to-org-use-id=. The default
setting for this variable is =create-if-interactive=, meaning
that an ID will be created when you store a link interactively,
but not if you happen to be in an Org-mode file while you create
a remember note (which usually has a link to the place where you
were when starting remember).
Org-mode still has a few operations that do not work well when the
first line of a buffer is a headline. One was constructing the clock
table, but this one is eliminated by this patch.
This patch compacts the persistence code. It also make sure that no
variables outside Org's name space are created. Finally, it makes
sure that the resumed clock is not hidden after a restart of Emacs.
Saving the clock history and the running clock could lead to pointers
to non-existing buffer, or to dired buffers of directories. This
patch implements more consistency checks.
It also allows a new value for `org-clock-persist'. When this is
`clock', only the running clock, but not the entire clock history
is saved.
Org-mode produces summaries of clocked items in the form of Org-mode
tables. This patch implements the possibility to define formulas that
should be applied to the clock tables, in order to do additional
analysis.
Formulas for clock tables are supported in two ways.
First, a formula can simply be added by hand to a table. Part of this
patch makes sure that, when the previous version of the table contains
a #+TBLFM: line, it will be copied to the new version.
Secondly, the clocktable definition allows a new parameter
`:formula'. The string value of this parameter will be installed as
the formula line for the table. If a formula parameter is given, it
will overrule any previous formula line.
As a special case, using the symbol `%' as the formula will install a
formula that will compute the fraction of total time that was spent in
a subtree.
In both cases, the formulas will be immediately evaluated after the
table has been created.
