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ACE2 (originally AppJet Code Editor)
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(This doc started Dec 2009 by dgreenspan.)

ACE2 is EtherPad's editor, a content-editable-based rich text editor
that supports IE6+, FF(2?/)3+, Safari(3?/)4+.  It supports
collaborative editing using operation transforms (easysync2),
undo/redo, copy/paste.

The name "ACE2" is because this is a rewrite of aiba's original
content-editable AppJet Code Editor.

== Building it

In this directory, run `bin/make normal etherpad` (requires scala),
which generates `build/ace2.js` and copies this and other files into
the etherpad source tree.  To have the script keep running and
automatically rebuild when source files change, run `bin/make auto
etherpad`.

The original reason for the build process was that ACE needs to
construct two nested iframes on the client, and to do this without
incurring round-trips to the server, it programmatically loads code
into the outer iframe that loads code into the inner iframe; so the
bulk of ACE's code is compressed into a string literal (twice).  Later
on, refactoring meant that the source is also divided into more than a
dozen files that the build script combines, and some are also
server-side EtherPad modules or client-side libraries (or both).

The master copy of the operational transform (OT) library, easysync2,
lives here.

In the early days it was possible to run ACE in a sort of development
mode, without the compression and iframe injection, by running it out
of the 'www' directory, but this is no longer possible.

== Browser support

We went out of our way to support IE6+.  IE's design-mode is quite
robust, though there are some differences in manipulation of the
selection and insertion point and in the DOM representation we had to
use.

We don't support Opera.  Opera is a problematic case, because
apparently JS running in different iframes is run concurrently, not
linearized into a single event thread.  This seems to be a rather
obscure fact and is almost difficult to believe.  As if iframes don't
complicate scripting enough!

== Syntax highlighting

Though syntax highlighting predated rich text as the original
motivation for the design of ACE, support was eventually dropped in
EtherPad.  At first the plan was to generalize it to other programming
languages, but the task was deprioritized (and difficult), and during
subsequent optimization and refactoring of ACE, calls to the
incremental lexer were stripped out because they complicated things.

One plan for multi-language syntax highlighting, never implemented,
was to calculate syntax highlighting on the server as a sort of "style
overlay" and feed updates to the client along with updates to the
document text.

== Changeset format

See easysync-notes.txt for some notes on the changeset format, which
was redesigned with the advent of rich text.