Html5.org is built with the following tech stack:
Document Encoding
UTF-8
UTF-8 (8-bit UCS/Unicode Transformation Format) is a variable-length character encoding for Unicode. It is the preferred encoding for web pages.
Document Standards
HTML5 DocType
The DOCTYPE is a required preamble for HTML5 websites.
HTML 5 Specific Tags
This page contains tags that are specific to an HTML 5 implementation.
Content Type Options
Used to disable MIME-sniffing for a particular HTTP response.
Strict Transport Security
The HTTP Strict-Transport-Security (HSTS) header instructs the browser to only use https.
SSL Certificates
HSTS
Forces browsers to only communicate with the site using HTTPS.