Documentation request for “default” layout handling

[lanoxx]

I would like to clarify how clients of ibus should handle the “default” layout that ibus passes for certain input sources such as sunpinyin.

Which of the following three options would correctly handle a “default” layout:

1. Keep layout as is, for example if layout was “de”, then it will still be “de” after “sunpinyin” has been activated.
2. Change layout to “us” as a general default.
3. Determine the default layout for the user (e.g the layout corresponding to the native keyboard layout) and use that as default?

I am not sure if 3. is currently possible, since I think the user does not configure a default but we could use the first layout from the list of configured layouts.

[fujiwarat]

It means 1. the layout is not changed. I think the layout "" would be better than "default".
Probably it's good to describe in ibus_engine_desc_new() and ibus_engine_desc_new_varargs().