interface CaptionTrack {
  id: string;
  format: 'vtt' | 'srt';
  content: string;
  duration: number; // seconds
}

function validateCaptionTrack(track: CaptionTrack): ValidationResult {
  const errors: string[] = [];
  const lines = track.content.split(/\r?\n/);
  
  // Check for WebVTT header if format is vtt
  if (track.format === 'vtt' && !lines[0].startsWith('WEBVTT')) {
    errors.push('Missing WEBVTT header');
  }

  // Verify timing cues exist and are properly formatted
  const timingRegex = /(\d{2}:\d{2}:\d{2}\.\d{3})\s*-->\s*(\d{2}:\d{2}:\d{2}\.\d{3})/;
  let cueCount = 0;
  let hasSpeakerTags = false;

  for (const line of lines) {
    if (timingRegex.test(line)) {
      cueCount++;
    }
    if (line.includes('<v ') || line.includes('Speaker:')) {
      hasSpeakerTags = true;
    }
  }

  if (cueCount === 0) errors.push('No valid timing cues detected');
  if (track.duration > 60 && !hasSpeakerTags) {
    errors.push('Multi-speaker content requires speaker identification tags');
  }

  return {
    valid: errors.length === 0,
    errors,
    metadata: { cueCount, hasSpeakerTags, format: track.format }
  };
}

interface PDFAsset {
  filename: string;
  buffer: Buffer;
  metadata: Record<string, unknown>;
}

async function validatePDFStructure(asset: PDFAsset): Promise<ValidationResult> {
  const errors: string[] = [];
  
  // Simulate text layer extraction check
  const hasTextLayer = await extractTextLayer(asset.buffer);
  if (!hasTextLayer) {
    errors.push('PDF lacks selectable text layer; image-only exports are non-compliant');
  }

  // Verify tab order and form field semantics
  const formFields = await extractFormFields(asset.buffer);
  if (formFields.length > 0) {
    const tabOrder = await extractTabOrder(asset.buffer);
    if (!isSequential(tabOrder)) {
      errors.push('Form fields lack sequential tab order');
    }
  }

  // Check for embedded image alt text
  const images = await extractImageMetadata(asset.buffer);
  const missingAlt = images.filter(img => !img.altText);
  if (missingAlt.length > 0) {
    errors.push(`${missingAlt.length} image(s) missing alt text attributes`);
  }

  return { valid: errors.length === 0, errors };
}

The validation layer intercepts these exports before they reach the student dashboard. Enforcing PDF/A-2b ensures that text encoding, font embedding, and metadata standards remain consistent across operating systems and assistive technologies. Tab order validation prevents screen readers from jumping between form fields in unpredictable sequences, which is a common failure point in downloadable worksheets.

Step 3: Marketing Asset Sanitization

Sales pages and transactional emails require semantic HTML validation. The pipeline should strip autoplay attributes, enforce descriptive button text, and replace image-based CTAs with native HTML elements.

interface MarketingAsset {
  type: 'sales_page' | 'onboarding_email';
  html: string;
}

function sanitizeMarketingAsset(asset: MarketingAsset): SanitizationResult {
  const warnings: string[] = [];
  let sanitizedHtml = asset.html;

  // Remove autoplay audio/video
  if (/autoplay\s*=\s*["']?true["']?/i.test(sanitizedHtml)) {
    sanitizedHtml = sanitizedHtml.replace(/autoplay\s*=\s*["']?true["']?/gi, '');
    warnings.push('Removed autoplay attribute to prevent WCAG 1.4.2 violation');
  }

  // Enforce descriptive button text
  const buttonRegex = /<button[^>]*>(.*?)<\/button>/gi;
  sanitizedHtml = sanitizedHtml.replace(buttonRegex, (match, text) => {
    const cleanText = text.trim().toLowerCase();
    if (['click here', 'buy', 'submit'].includes(cleanText)) {
      warnings.push(`Button text "${text}" lacks descriptive context`);
      return match.replace(text, 'Enroll in Course');
    }
    return match;
  });

  // Validate email link semantics
  if (asset.type === 'onboarding_email') {
    const linkRegex = /<a[^>]*href="([^"]+)"[^>]*>(.*?)<\/a>/gi;
    sanitizedHtml = sanitizedHtml.replace(linkRegex, (match, href, text) => {
      if (href === text || text.length > 50) {
        warnings.push('Long or raw URL used as anchor text');
        return match.replace(text, 'Access your course dashboard');
      }
      return match;
    });
  }

  return { sanitizedHtml, warnings };
}

Architecture Rationale: Marketing assets are the primary entry point for enrollment transactions. WCAG 2.2 requires that all interactive elements be operable via keyboard and convey clear purpose. Autoplay audio violates WCAG 1.4.2 (Audio Control) and triggers immediate compliance flags. Replacing image-based buttons with semantic <button> elements ensures that screen readers announce actionable controls correctly. Email sanitization prevents broken anchor text patterns that confuse assistive technology users during onboarding sequences.

Step 4: Automated Pre-Publish Compliance Gates

The final step integrates validation results into the publishing workflow. Assets that fail validation are quarantined until remediation is complete. This prevents non-compliant content from reaching production environments.

type ComplianceStatus = 'pending' | 'passed' | 'failed' | 'quarantined';

interface PublishGate {
  assetId: string;
  status: ComplianceStatus;
  validationReport: ValidationResult;
  lastChecked: Date;
}

async function evaluatePublishGate(gate: PublishGate): Promise<PublishDecision> {
  if (gate.validationReport.valid) {
    return { allowed: true, reason: 'All WCAG 2.2 AA checks passed' };
  }

  const criticalErrors = gate.validationReport.errors.filter(
    err => err.includes('text layer') || err.includes('autoplay') || err.includes('timing cues')
  );

  if (criticalErrors.length > 0) {
    gate.status = 'quarantined';
    return { 
      allowed: false, 
      reason: 'Critical compliance failures detected. Asset quarantined until remediation.',
      blockedBy: criticalErrors 
    };
  }

  gate.status = 'failed';
  return { 
    allowed: false, 
    reason: 'Non-critical warnings detected. Manual review required.',
    warnings: gate.validationReport.errors 
  };
}

Architecture Rationale: Pre-publish gates enforce shift-left compliance. By quarantining assets with critical failures, the system prevents legal exposure while allowing non-critical warnings to proceed to manual review. This balances operational velocity with regulatory adherence. The gate integrates with CI/CD pipelines or CMS publishing workflows, ensuring that compliance is evaluated consistently across all content types.

Pitfall Guide

1. Auto-Caption Reliance

Explanation: Platform-generated captions are optimized for speed, not accuracy. They frequently misinterpret technical terms, merge speaker changes, and omit environmental audio cues. Fix: Implement a verified caption pipeline. Use professional transcription services or AI models with domain-specific fine-tuning, followed by human review. Export to .vtt and validate timing cues before ingestion.

2. Image-Only PDF Exports

Explanation: Design tools often export PDFs as flattened images. Screen readers cannot extract text, and users cannot search or copy content. Fix: Export from source documents using "Accessible PDF" or "PDF/A" presets. Verify text selection capability in Acrobat or Sejda. Inject alt text for all embedded images before distribution.

3. Gradient Background Contrast Failures

Explanation: Page builders frequently apply text over gradient backgrounds without calculating luminance ratios. This creates invisible text for users with low vision. Fix: Run all theme variations through a contrast checker (minimum 4.5:1 for normal text, 3:1 for large text). Apply semi-transparent overlays behind text blocks to guarantee consistent contrast regardless of background image.

4. Autoplay Audio on Hero Sections

Explanation: Auto-playing video or audio with sound violates WCAG 1.4.2 and disrupts screen reader users. It also triggers browser autoplay policies that block media entirely. Fix: Disable autoplay by default. If autoplay is required for UX, mute audio and provide a visible, keyboard-accessible play control. Ensure media pauses when focus moves away from the player.

5. Email Link & Button Anti-Patterns

Explanation: Pasting raw URLs as anchor text or using images styled as buttons breaks semantic structure. Screen readers announce "link" or "image" without conveying purpose. Fix: Use descriptive anchor text ("Start Module 1" instead of raw URLs). Replace image buttons with native HTML <button> or <a role="button"> elements. Verify alt text on all embedded email images.

6. Unmoderated UGC Liability

Explanation: Community platforms host user-generated posts, comments, and media. While creators don't author this content, platform hosts remain responsible for WCAG 2.2 AA compliance at the infrastructure level. Fix: Implement content moderation filters that flag missing alt text, broken links, or inaccessible media in user submissions. Provide clear accessibility guidelines for community members and enforce platform-level keyboard navigation and focus management.

7. Missing Focus Indicators in Custom Themes

Explanation: Custom CSS frequently removes default :focus outlines to achieve visual minimalism. This breaks keyboard navigation for users who rely on tab-based interaction. Fix: Never use outline: none without providing an alternative focus style. Implement high-contrast focus rings using box-shadow or border that meet WCAG contrast requirements. Test all interactive elements using keyboard-only navigation.

Production Bundle

Action Checklist

• Audit all existing video assets and replace auto-captions with verified .vtt tracks
• Run PDF workbooks through a text-layer extraction tool; remediate image-only exports
• Disable autoplay audio on all sales pages and hero sections; verify mute-by-default behavior
• Replace image-based CTA buttons with semantic HTML elements across marketing templates
• Validate email anchor text and alt text attributes in onboarding and abandoned-cart sequences
• Implement pre-publish validation gates for media, documents, and marketing assets
• Conduct a 20-minute keyboard-only navigation audit of the enrollment flow and lesson dashboard
• Document accessibility standards in the content creation SOP and train production teams

Decision Matrix

Scenario	Recommended Approach	Why	Cost Impact
Solo creator with <50 videos	Manual caption review + PDF remediation	Low volume allows direct quality control without automation overhead	$25-$60/video
Mid-sized platform (50-500 videos)	Automated validation pipeline + professional transcription service	Balances scale with compliance accuracy; reduces manual review time	$0.50-$1.25/min + pipeline setup
Enterprise course marketplace	CI/CD compliance gates + AI-assisted captioning + human QA	High volume requires automated pre-publish checks to prevent non-compliant assets from reaching production	Pipeline development + ongoing QA
Community-driven platform	UGC moderation filters + platform-level WCAG 2.2 AA enforcement	User-generated content shifts liability to host; infrastructure must enforce baseline standards	Moderation tooling + accessibility engineering

Configuration Template

# compliance-gate.yml
# Pre-publish validation configuration for digital course assets

media:
  caption_format: vtt
  min_accuracy_threshold: 0.98
  require_speaker_tags: true
  max_auto_caption_rejection: true

documents:
  pdf_standard: PDF/A-2b
  require_text_layer: true
  validate_tab_order: true
  enforce_image_alt_text: true

marketing:
  disable_autoplay_audio: true
  require_descriptive_buttons: true
  sanitize_email_links: true
  min_contrast_ratio: 4.5

publishing:
  quarantine_on_critical_failure: true
  allow_non_critical_warnings: true
  audit_log_retention_days: 365
  webhook_on_compliance_failure: "https://api.yourplatform.com/webhooks/compliance-alert"

Quick Start Guide

1. Initialize Validation Pipeline: Clone the compliance gate repository and configure the compliance-gate.yml template to match your asset types. Deploy the validation service to your staging environment.
2. Ingest Existing Assets: Run a batch scan of current video, PDF, and marketing assets. Quarantine any files that fail critical checks (missing text layers, auto-captions, autoplay audio).
3. Remediate & Revalidate: Process quarantined assets through verified caption services, PDF remediation tools, and HTML sanitization scripts. Re-run validation until all assets pass.
4. Enable Pre-Publish Gates: Activate the compliance gate in your CMS or publishing workflow. Configure webhooks to alert content teams when assets fail validation.
5. Schedule Quarterly Audits: Automate a recurring scan of published content. Update validation rules as WCAG guidelines evolve and platform features change.