Framework to develop own forms/UI designer

I have application which consumes XML and based on this creates a GUI. Basically this is declarative language in form of XML to design the GUI. Now I want to create a visual GUI designer to edit forms and screens on the screen and output will be that XML.

I need a suggestion what can help me in my development, may be there is some kind of framework already exist (Java or XHTML/JavaScrip开发者_开发问答t or Flash/Flex platforms even may be Eclipse Plugin?) or may be there some open source tools are out there?

Thank you.

OpenLaszlo is a declarative UI framework. And there is a project for an IDE in Eclipse. It could help you...