1. A method for composing a user-defined web page, comprising: at a client, using a web browser executed at the client: displaying in a first browser window an authoring web page, including displaying a graphical user interface of an authoring tool that is embedded in the authoring web page; the displayed graphical user interface for composing the user-defined web page; using the displayed graphical user interface of the authoring tool to receive user instructions, and responding to the user instructions by placing instances of predefined structured fields in the user-defined web page and associating user-specified content with the instances of the predefined structured fields; and displaying a preview of the user-defined web page.