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Banner
A persistent situation that needs a decision — wide, inline, and never blocking.Choose it deliberately
Use the component when its contract matches the user task.
Use when
A page or section situation persists and needs a visible decision: setup, offline, changed terms.
Avoid overloading
Severity belongs to MAlert, transient feedback to MSnackbar, blocking choices to a dialog.
Composition
Sizing, labels, and neighboring elements should preserve visual hierarchy.
One primary meaning
One situation per banner; several stacked banners signal a deeper product problem.
Placement is external
The banner has no sticky prop: compose it with the layout family when placement matters.