IsInstalled not properly documented

[AndreRicardo-Zoetis]

Can you please help understand in what cases "IsInstalled" is called?

The documentation https://github.com/Azure/iot-hub-device-update/blob/develop/docs/agent-reference/how-to-implement-custom-update-handler.md states "In some situation", which situations?

[jw-msft]

Acknowledged. That documentation is vague--thanks for calling this out. In general, the "contract" is that it can be called an unspecified number of times during the deployment process so it should avoid being an expensive operation or at least results of first call should be cached for subsequent calls.

The doc should be clarified to show exactly where/when to expect IsInstalled to be called and a doc for IsInstalled authoring guidance (e.g. the overall StepsHandler layer's IsInstalled state should be a conjunction of each step's contentHandler IsInstalled calls and contentHandler IsInstall is scoped to installed state of that handler's content).