doc/robots.txt

User-agent: *
Disallow: /en/4.2.x/
Disallow: /ja/4.2.x/
Disallow: /en/5.3.x/
Disallow: /ja/5.3.x/
Disallow: /en/6.1.x/
Disallow: /ja/6.1.x/
Disallow: /en/6.2.x/
Disallow: /ja/6.2.x/