Function extractCanonical

extractCanonical(input: DocumentInput): CanonicalMetadata
Extract canonical and alternate URL metadata from HTML.
Parameters
- input: DocumentInput
  Parsed HTML document or raw HTML string
Returns CanonicalMetadata
Canonical metadata object
Remarks
Extracts canonical URLs, language alternates, AMP versions, manifests, and app linking metadata.
Example
```
// With parsed document (recommended for multiple extractions)
const doc = parseHTML(htmlString);
const canonical = extractCanonical(doc);

// Or directly with HTML string
const canonical = extractCanonical(htmlString);
```
- Defined in src/metadata/canonical/extract.ts:39