The standard client is also capable of being extended by customers, to allow the addition of custom tools. The custom tools are built with Adobe Flash Builder as SWF files, and may include map interaction and custom dialogs. The custom SWF is loaded and managed by the Dekho application, hence it is shown within the Dekho application in the diagram, although technically they run side-by-side in the ActionScript virtual machine.
The Dekho flex extensions API provides a basis for custom tools to communicate with the Dekho client. The custom tool can interact with Dekho in a few different ways; as well as Dekho Web Services, Dekho broadcasts and messages, the Flex Extension API allows for calls to functions in the Dekho client. The functions that can be called are limited as most required interaction can be done via the Web Services and messaging. The Dekho client also calls any custom tools to pass messages to it (see the Messages section for details on the messages that can be sent).
As well as this documentation, sample code is available from ESRI Australia.