[webkit-dev] New approach for DOM attributes that reflect content attributes

[Darin Adler]

There are many attributes in the DOM that are simply covers for  
getting and setting HTML or SVG attributes. The HTML 5 draft calls  
this reflection of content attributes.

Currently we do this by writing getter and setter functions. For  
example, see the placeholder and useMap attributes of HTMLInputElement.

A better way to do this is to declare that the attribute reflects a  
content attribute in the .idl file, and have the bindings call  
setAttribute and getAttribute directly. I plan to do this, with the  
following syntax. This indicates that the title attribute reflects a  
content attribute named title:

     attribute [Reflect] DOMString title;

This indicates that the className DOM attribute reflects a content  
attribute named class:

     attribute [Reflect=class] DOMString className;

This indicates that the src DOM attribute reflects a content attribute  
named src, but that the result is a completed URL, not the raw  
attribute value:

     attribute [ReflectURL] DOMString src;

I’m going to begin this work with this bug <https://bugs.webkit.org/show_bug.cgi?id=25425 
 >. That bug talks about a need to change the details of various  
getters and setters, and I decided it was better not to do this, but  
rather to have the getters and setters be auto-generated.

I will implement this for the JavaScript bindings and Objective-C  
bindings, but someone else will have to take care of the V8 bindings.

Once the bindings are working, I plan to remove the functions in the  
DOM implementation classes. So I would delete the  
HTMLInputElement::placeholder and HTMLInputElement::setPlaceholder  
functions once the [Reflect] attribute has been used for them.

For now I will begin by implementing [Reflect] and using it in a few  
places, but I won’t delete any functions from the DOM implementation  
classes yet.

     -- Darin