A Module is a component which displays UI and runs as part of a Story.
Multiple modules can be composed into a single story, and modules can add other modules to the story they are part of. Module's can either embed other modules within their own content, or they can delegate visual composition to the StoryShell.
A module is given access to two services provided by the modular framework in its incoming namespace:
fuchsia.modular.ComponentContext which gives the agent access to functionality which is shared across components run under the modular framework (e.g. modules, shells, agents).fuchsia.modular.ModuleContext which gives modules access to module specific functionality, like adding other modules to its story and creating entities.A module is expected to provide three services to the modular framework in its outgoing namespace:
fuchsia.ui.app.ViewProvider which is used to display the module's UI.fuchsia.modular.Lifecycle which allows the framework to signal the module to terminate gracefully.fuchsia.modular.IntentHandler which allows the framework to send intents to the module.A module's lifecycle is bound to the lifecycle of the story it is part of. In addition, a given module can have multiple running instances in a single story.
When a module starts another module it is given a module controller which it can use to control the lifecycle of the started module.
Modules communicate with other modules via intents and entities, and with agents via FIDL and message queues.