What is the best option for creating an in-browser UI-editor?

Question

I want to create an simple UI-editor that can be used within the browser. It basically should have a UI-control palette and a canvas to layout and modify the controls. The resulting user-created UI model should be stored in some kind of backend and comply to an (abstract) UI description language (e.g. XForms). The UI-model should be downloadable as file (e.g. XForms document). A visual in-browser XForms-designer is probably a good example of what I want to achieve. The UI-editor should be usable cross browser.

Please keep in mind that i mentioned XForms only as an example. I don't want to rely on the browsers capabilities wrt. my target model. The target model (e.g. XForms) should only be used as storage format. The cross browser rendering of the desgin-time UIs in the editor should be ensured by the toolkit/framework.

Possible canditates are probably:

• GWT
• Adobe Flex 3
• Eclipse RAP

The UI-editor will not be used in production. My focus lies on a rapid development of the editor.

Answer 1

The extjs JavaScript library is good for implementing GUIs in JavaScript. It can also be used with Adobe AIR or Google Gears for creating offline applications, and works well with different browsers.

Here is an example of a GUI editor for extjs: http://tof2k.com/ext/formbuilder/