chore: clarify event/domain scoping, lifecycle (#248)

Adding some additional non-normative text to clarify a few things at the
prompt of @federicobond .

The meaning and justification should be self-evident, and if it's not I
did a bad job. 😅

---------

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

specification/glossary.md

@@ -28,6 +28,7 @@ This document defines some terms that are used across this specification.
   - [Evaluation API](#evaluation-api)
   - [Flag Management System](#flag-management-system)
   - [Provider](#provider)
+  - [Provider Lifecycle](#provider-lifecycle)
   - [Domain](#domain)
   - [Integration](#integration)
   - [Evaluation Context](#evaluation-context)
@@ -109,9 +110,13 @@ A source-of-truth for flag values and rules. Flag management systems may include
 
 An SDK-compliant implementation which resolves flag values from a particular flag management system, allowing the use of the [Evaluation API](./sections/01-flag-evaluation.md#13-flag-evaluation) as an abstraction for the system in question.
 
+### Provider Lifecycle
+
+The possible states and transitions of a provider over the course of its usage, as defined by the [provider interface](./sections/02-providers.md).
+
 ### Domain
 
-An identifier which logically binds clients with providers, allowing for multiple providers to be used simultaneously within a single application.
+An identifier which logically binds clients with providers, allowing for multiple providers to be used simultaneously within a single application. Domain binding is dynamic; it may change over the course of an application's lifetime (ie: a client associated to the default provider via an unbound domain will be bound to a new provider if a provider is subsequently assigned to that domain).
 
 ### Integration
 

specification/sections/05-events.md

@@ -22,6 +22,11 @@ graph
     C -->|run handlers| CH(Client event handlers)
 ```
 
+The `domain` of a provider constitutes a logical scope for events.
+Clients associated to a particular provider through a `domain`, run event handlers only when that provider emits events, or one of its lifecycle functions terminates.
+
+see: [domain](../glossary.md#domain)
+
 ### 5.1. Provider events
 
 #### Requirement 5.1.1
@@ -44,13 +49,17 @@ see: [provider event types](../types.md#provider-events), [`event details`](../t
 
 > When a `provider` signals the occurrence of a particular `event`, the associated `client` and `API` event handlers **MUST** run.
 
+Client event handlers respect the dynamic binding of clients to providers via `domains`.
+Client event handlers run when a lifecycle function terminates on the associated provider, or the associated provider emits an event. 
+
 see: [provider event types](./../types.md#provider-events) and [event handlers](#52-event-handlers).
 
 #### Requirement 5.1.3
 
 > When a `provider` signals the occurrence of a particular `event`, event handlers on clients which are not associated with that provider **MUST NOT** run.
 
-Providers bound to a `domain` constitute their own "events scope".
+Client event handlers respect the dynamic binding of clients to providers via `domains`.
+Client event handlers do not run when a lifecycle function terminates on an unassociated provider, or an unassociated provider emits an event. 
 
 see [setting a provider](./01-flag-evaluation.md#setting-a-provider), [domain](../glossary.md#domain) for details.
 
@@ -130,6 +139,7 @@ This means that the order of provider configuration and event handler addition i
 ### Event handlers and initialization
 
 Though providers themselves need not implement events, the `flag evaluation API` uses events to convey relevant state changes during configuration and initialization.
+Implementations automatically emit `PROVIDER_READY` or `PROVIDER_ERROR` events depending on the outcome of the `initialize` function, if the provider has implemented one (if none is implemented, `PROVIDER_READY` runs unconditionally).
 _Application authors_ and _application integrators_ use these events to wait for proper initialization of the provider and to do basic monitoring and error handling.
 
 #### Requirement 5.3.1