== Component Model (aka XBL2) Use Cases ==

A canonical set of uses cases that represents the set of problems we are trying to solve by implementing a component model. For implementation details, see [http://dev.w3.org/2006/xbl2/Overview.html XBL2 Spec].

=== Built-in HTML Elements and Their Behaviors ===

Does:
 * provide a uniform way to browsers to implement complex HTML elements, such as video/audio, sliders, progress elements, etc. possibly using scripting.
 * provide light-weight implementations of specialized markup languages

Need:
 * UA-level attachment
 * Ability to completely hide implementation from consumer
 * Restricted post-UA-level styling using pseudoclasses
 * High performance

Don't care:
 * mutable templates
 * dynamic attachment/detachment
 * template inheritance
 * attachment using CSS or DOM
 * content element (output ports), since they can't have children (this may change)

=== Custom User Interface Widget System ===

Build a widget system that allows the following:
 * asynchronously instantiate and initialize widgets
 * for instance, display a widget without starting up a script context, then progressively enhance with script.
 * seamlessly reuse widget written using various libraries or frameworks
 * use widgets declaratively, with minimal knowledge of the underlying implementation
 * provide a uniform way (i.e. DOM) to declare widget APIs

=== Layout Manager ===

 * make easier the restructuring of content to accommodate layout, both in an imperative and a declarative way
 * enable development of templating/theming frameworks