Currently the URL elements of various Xero resources appear to reject URLs that do not fit the http or https scheme. It would be very helpful if this barrier was removed.

Both OS X and iOS are seeing an explosion of applications that implement custom URL schemes as a way to hook or callback. https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/Inter-AppCommunication/Inter-AppCommunication.html

My personal use case is a custom built warehouse management system. Our established application is hosted on premises, with client runtimes on OS X and iOS. We're integrating as a private app to Xero and will be pushing in contacts, payables and sales. All of these will retain supporting detail in our existing system. Allowing a URL to our custom scheme could give Xero interfaces 1-click navigation back into corresponding records in our system.