Value prop

A progress bar draws its progress rather than writing it, so nothing in its anatomy stands for the value. Which prop carries it is declared in config/conventions/specs.yaml.

value:
  prop: percent
  indeterminate: isIndeterminate

prop names the prop carrying the value. A generated component binds it to the value attribute the resolved role calls for — aria-valuenow on a progress bar, for instance.

An element beats a prop

Where a value part role resolves, it wins, for the same reason a label element beats an accessible-name prop.

indeterminate

A boolean prop that forces the indeterminate presentation regardless of the value. Resolution runs in order:

1. indeterminate is true — the value is suppressed
2. otherwise prop resolves — the determinate form is emitted
3. otherwise the indeterminate form is emitted, with a warning

Why this is not a state concept

The state concepts are a governed vocabulary, each resolving to a canonical selector, and indeterminate there already means a checkbox’s mixed state — :indeterminate, aria-checked="mixed".

A progress bar with no known value is a different fact wearing the same word. It suppresses aria-valuenow and has no selector at all. Folding the two would widen a governed vocabulary to absorb a prop binding, which is what the governance exists to prevent — so it is modelled as what it actually is: a property of the value.

See Also

• Accessibility props — the same idea for an accessible name
• States — the governed state vocabulary
• value role — where an element represents the value instead