- A browser behavior where the rendering engine switches between different parsing and layout modes based on the doctype declaration at the beginning of an HTML document. When a valid HTML doctype (
<!DOCTYPE html>) or other standards-compliant doctype is present, browsers render in “standards mode,” following modern web standards, while missing or invalid doctypes trigger “quirks mode,” which emulates legacy browser behaviors for backward compatibility. The mechanism allows browsers to handle both modern standards-compliant websites and older websites designed for outdated browser behaviors.
- Related terms: Doctype · No-quirks mode · Quirks mode · Limited-quirks mode
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