For AI agents and LLMs: a machine-readable index is available at llms.txt. A plain-Markdown version of any documentation page is available by appending .md to its URL.
Skip to main content

Invalid Range Values

Range controls — sliders, steppers, progress indicators — must report a valid, consistent value so VoiceOver can announce their state correctly.

WCAG Reference

Maps to: WCAG 4.1.2 Name, Role, Value | Applies to: WCAG 2.0, WCAG 2.1, WCAG 2.2 Introduced in: WCAG 2.0 | Level: A | Read the official specification →

What this rule checks​

The scanner checks range controls (Slider, Stepper, ProgressIndicator) and any custom view with the .adjustable trait for two types of violation:

  1. Missing value — the control has no programmatic accessibilityValue, so VoiceOver cannot announce its current state.
  2. NaN value — a native UISlider whose minimumValue >= maximumValue produces a NaN accessibility value (UIKit computes (value - min) / (max - min), which yields NaN when the denominator is zero or negative).

Why it matters​

Assistive technology announces a range control's position from its reported values ("50 percent"). When the value is missing, VoiceOver says nothing about the control's state. When the value is NaN (due to an invalid min/max range), the announcement is meaningless, and adjusting the control by voice or gestures produces unpredictable results.

Common failure patterns​

  • custom views with the .adjustable trait that never set accessibilityValue
  • a UISlider whose minimumValue is set higher than its maximumValue
  • a UISlider whose minimumValue equals its maximumValue (zero-width range)
  • progress indicators or steppers with no programmatic value for assistive technology

Remediation guidance​

  • ensure min < max and the current value falls within [min, max] on the control (UISlider/UIStepper)
  • for custom range controls, expose the range to assistive technology via accessibilityValue and the .adjustable trait

Limitations​

  • NaN detection only. Detection of min >= max relies on NaN in UIKit's auto-computed accessibilityValue. If a developer manually overrides accessibilityValue on a broken slider, the NaN is masked and the violation goes undetected.
  • Cannot detect current outside [min, max]. iOS normalizes the slider value to a percentage and does not expose raw min, max, or current values individually.
Last updated on

Test across 3000+ combinations of browsers, real devices & OS.

×
Schedule Your Personal Demo
Book Demo

Help and Support

Related Articles

On this page