It is sometimes useful to write standalone web applications that can be shared across offices or with other users; these applications would need an intuitive user interface. This chapter will teach you how to build these interfaces.

If you are a Google Docs user (and if you read this book, you certainly will be), you probably like the ability to share documents with friends or co-workers, but you would sometimes like the option to not share every part of it.

For example, it would be nice for one to be able to see data about themselves on a spreadsheet, but not all the data about everyone. As we experienced before, spreadsheets, for example, can be selectively write-protected, but there is no way to hide ranges selectively depending on the user viewing it.

We could imagine some workaround by copying part of the sheet to a new one and sharing this one, but then we'd have to take care to synchronize these sheets. When we have many people...