At our March meeting, we started by comparing the document type declaration in a typical HTML4 webpage with the doctype now used in HTML5: <!doctype html >.
To understand why we can use that doctype now, we worked on seeing what the doctype actually does and how it relates to validation and to the appearance of a webpage.
We used a sample HTML file, swapped out doctypes, added and deleted errors, and then validated the file using different doctypes. The result was that the browser (Firefox) displayed the page the same way with each version, while the validator showed different errors each time.
Next month,we will have a couple of final points on this topic before moving on.
The validator we used is at the W3C website.
For more on doctypes, see this somewhat dated article at the W3C site.