Doctype Descriptions - This page contains the Basic Doctypes (Which is the type of HTML code you're using, such as HTML 4.01, and the RULES behind it. Keep this in mind. Some do things that others do not. You will find out when you read it.) that you can/will be using to create your web page. I assume we'll be using HTML 5, but it is -always- good to know where that came from and how it got to where it is, what it can do and what sets it apart from the other types.
HTML Elements Table - This is a -very- useful chart in that page link abouve. It lists exactly what each Doctype CAN and CANNOT Do.
I've said it once, and I'll say it again: I love this site! ^_^ For those of you who've never written any kind of HTML or XHTML code, this is a great place to start. It's one thing to know the "How" but it's a complete other to know the "Why" and I always encourage knowing the "Why" so that you can properly utilize your tools.
For the more advanced users and those who wish to do a little more coding, this page contains a few more Doctypes such as MathML Doctype Declarations, that can come in quite handy with their extra power: (X)HTML Doctype Declarations List
Take Note! HTML 5 is -NOT- a Standard HTML Source yet! 4.01 is still the main standard! - The reason being: Where it is powerful (easy use of video and audio files within a webpage: therefore it supports them and you don't need a host + code to run said files within it) it is still too new to be part of the mainstream. Most businesses are likely hesitant to make that change, especially due to the fact that 4.0 does the exact same things, or simply do not know about it yet. However, HTML 5 -is- the future and much easier to use with today's content, so those businesses that invest in it are likely to get a lot more out of it in the long run: imo.
Hope this helped and I didn't let on too much of my own views! ^_^
~Astra~