Provides a set of interfaces and classes for debug context management.

## Package Specification

This package provides a set interfaces and classes to manage debug contexts.

A debug context represents an active state of a program being debugged. The active debug context drives the enabled state of debug actions (step, terminate, etc.), source lookup, visible variables, watch expression values, etc. The debug platform allows clients to register for context change notification in order to respond to changes in the active debug state, as well as register context providers that drive the active debug state. The debug platform has context listeners and providers itself. For example, the debug platform's stepping actions register for context change notification to update enabled state and the Debug view registers as a context provider.

There can be any number of debug contexts within a workbench window, but at any one time there is only one active debug context within a part and one active context within a workbench window. The debug platform provides a debug context service per window (`IDebugContextService`) that allows clients to register context providers for that window, and register for change notification within the window or a specific part in the window. If there is only one context provider in a window, it provides the context for the entire window as well as its part. If there is more than one context provider for a window, the context provider associated with the most recently active part provides the context for that window. It is possible to register a context provider that has no associated part. Only one such context provider can be registered with each service (window). A context provider that has no associated part provides context for its window only if there are no other context providers registered for that window.

A debug context is represented by a selection (`ISelection`). This allows for single or multi-element selections as well as text selections to provide context. Listeners are notified of context changes with debug context events (`DebugContextEvent`) . An event specifies the context that has changed and a bit mask describing how the context has changed. The platform defines two types of changes - activation and state change. An activated state indicates a new context - for example a thread suspending at a breakpoint or after a step. An activation triggers variables to refresh, source lookup, etc. A state change indicates that a previously activated state has changed. For example, a stack frame or thread that was activated has completed an implicit evaluation. A state change triggers action enabled states to update.