A major mode for creating and editing stand-off markup, also called
external markup.  It is written for use in the field of digital
humanities and the manual annotation of training data for
named-entity recognition.

After switching a buffer's major mode to standoff-mode, it gets
read-only. We then call it the source document, which the external
markup refers to. There are commands for creating 1) markup
elements, 2) relations between such elements that take the form of
RDF-like directed graphs, 3) attributes of markup elements and 4)
writing free text comments anchored on these elements. Markup
elements refer to portions of the source document by character
offsets.

There are several pluggable backends for storing the
annotations. They can be stored in JSON format or as elisp
s-expressions. The API for backends is defined in
`standoff-api.el'.

Usage:

Add the following lines to your Emacs config:

 (add-to-list 'load-path "/path/to/standoff-mode-directory")

 (autoload 'standoff-mode "standoff-mode.el"
   "Mode for creating and editing stand-off markup, aka external markup" t)

 ;; auto-load standoff-mode for files ending with .TEI-P5.xml:
 (add-to-list 'auto-mode-alist '("\\.TEI-P5.xml$" . standoff-mode))

You also have to choose a backend for storing the annotations. See
standoff-dummy.el or standoff-json-file.el for instructions.