>      for WebKit Xwidgets, both
>> for WebKitGTK impl and NS/mac impl.
> 
> Can you tell me what this has to do with Javascript?
> Is Webkitgtk implemented using Javascript?
No, but it’s a Javascript enabled web rendering engine,
and it provides API to interact with its Javascript interpreter.

> 
>> The script message handler API makes it possible to trigger event in emacs
>> from JavaScript, and can be used to implement procedure calling from
>> js to elisp. Currently only the other way around is possible.
> 
> If the Javascript code is free, or user-written, there's no harm in doing such
> calls in either direction.  But when the language is Javascript, given the way
> Javascript is usually used (running nonfree programs that random sites send,
> often in obfuscated form), I'm concerned that we are opening the door
> to vicious habits that we ought to be trying to discourage.
The Webkit itself supports Javascript and in current form that it's embedded in
Emacs, it either allows any Javascript execution, or Javascript can be completely 
disabled. This patch is about exposing more APIs to interact with Javascript,
and can be possibly used to control Javascript execution. 

I’m currently reading the source of librejs. It’s also written in 
Javascript and look like to let it run in Emacs and supervise the Webkit Xwidgets,
bidirectional calling between Elisp/JS is a necessity — which this patch
provides.