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Web Accessibility Utility Functions

Source: R/web_accessibility_utils.R
calculate_contrast_ratio.Rd

Functions for ensuring WCAG 2.1 Level AA compliance in the Shiny application

Calculates the contrast ratio between two colors according to WCAG 2.1 standards using the relative luminance formula from W3C guidelines. Used to verify text/background color combinations meet accessibility requirements.

Usage

calculate_contrast_ratio(foreground, background)

Arguments

foreground

Foreground color (hex format, e.g., "#111827")

background

Background color (hex format, e.g., "#ffffff")

Value

Numeric contrast ratio (1-21)

WCAG 2.1 Level AA Compliance

This package follows Web Content Accessibility Guidelines (WCAG) 2.1 Level AA:

  • 1.1.1 Non-text Content (Level A): Alt text for images and visualizations

  • 1.4.3 Contrast Minimum (Level AA): 4.5:1 ratio for normal text, 3:1 for large text/UI

  • 2.1.1 Keyboard (Level A): Full keyboard navigation support

  • 2.4.1 Bypass Blocks (Level A): Skip navigation links

  • 3.1.1 Language of Page (Level A): Page language identification

  • 4.1.2 Name, Role, Value (Level A): ARIA labels and roles Calculate Color Contrast Ratio

WCAG Requirements

  • Normal text: Minimum 4.5:1 (Level AA)

  • Large text (18pt+ or 14pt+ bold): Minimum 3:1 (Level AA)

  • UI components and graphics: Minimum 3:1 (Level AA)

Examples

if (FALSE) { # \dontrun{
calculate_contrast_ratio("#111827", "#ffffff")  # Returns ~16:1 (Pass)
calculate_contrast_ratio("#6b7280", "#4a5568")  # Returns ~2.8:1 (Fail)
} # }