Virtualvfunc_emitted when the value of a UI widget changes. May trigger a
validity check via update_connection to write values to the connection.
Virtualvfunc_Virtualvfunc_called to save the user-entered options to the connection
object. Should return false and set error if the current options are
invalid. error should contain enough information for the plugin to
determine which UI widget is invalid at a later point in time. For
example, creating unique error codes for what error occurred and populating
the message field of error with the name of the invalid property.
Interface for implementing VpnEditor. Contains only the virtual methods that need to be implemented.