HTML
- HTML5
http://www.w3.org/TR/html5/
This specification defines the 5th major revision of the core language of the World Wide Web: the Hypertext Markup Language (HTML). - HTML 4.01 Specification
http://www.w3.org/TR/html4/
specification defines the HyperText Markup Language (HTML), the publishing language of the World Wide Web - HTML Tutorial - w3schools
http://www.w3schools.com/html/
This HTML tutorial contains hundreds of HTML examples.With our online HTML editor, you can edit the HTML, and click on a button to view the result. - HTML5 Doctor
http://html5doctor.com/
articles relating to HTML5, its semantics, and how to use it. - PageSpeed Insights
https://developers.google.com/speed/pagespeed/insights/
The PageSpeed tools analyze and optimize your site following web best practices. - The W3C Markup Validation Service
http://validator.w3.org/
W3C's easy-to-use HTML validation service, based on an SGML parser. - Webdesignérův průvodce po HTML5 - Zdroják
https://www.zdrojak.cz/serialy/webdesigneruv-pruvodce-po-html5/
Podrobněji a spíš z praktického hlediska, tedy „co můžeme začít používat a k čemu je to dobré“." - WebPagetest - Website Performance and Optimization Test
https://www.webpagetest.org/
Run a free website speed test from around the globe using real browsers at consumer connection speeds with detailed optimization recommendations.