#urinetrouble

This was the post that led me to learn that doctypes are no longer long and gross

A brief explanation of what the above really means:

DOCTYPE HTML is the tag that forces your webpage into the browser's "XHTML" rendering mode. If you're in "XHTML mode," most of the browser's built-in elements look different, and the text is in all caps. They also take the line breaks and indentation you put in when writing the document as part of the text — and not as markup that should be displayed on the page.

The tag above looks like a list of attributes. Among them, there are these:

DOCTYPE HTML

That is, it starts with the word "DOCTYPE" followed by a slash and the word "HTML." This tag causes your webpage to be displayed in this XHTML mode.

DOCTYPE HTML is an example of what's called a "document type declaration" (DTDL). They're an interesting thing to work with because they help you make sure that you have the right mode or modes on any specific webpage in the world.

XHTML and "XML" modes are not exactly compatible with each other. To write properly formatted, non-broken-up HTML and CSS on your webpage, you usually have to switch between the two at some point.

This is why it's helpful to have a way to specify the HTML mode as a whole for any one webpage, even if you don't use that XHTML mode in other pages (in which case you'd have to mess with the DOCTYPE HTML tag).

HTML mode is the default. You use the XHTML mode just when you want to format your webpage in a specific way, and you don't want to display your webpage in plain text (which is the default mode).

Most "basic" HTML documents start with the HTML mode:

DOCTYPE HTML

Headings should be in italics.

Paragraphs, like this one, are best broken up into two or more paragraphs.

And so forth.

HTML 5 adds the HTML5 tag:

#DOCTYPE html HTML5

HTML5 changes the default mode from HTML to HTML5. For instance, with HTML5, headings are in markdown, not italics, and paragraphs are automatically separated into chunks of no more than 72 characters.

#DOCTYPE HTML HTML5

HTML5 also adds two new tags to the "attributes" bit of that DOCTYPE HTML thing:

#encoding

#standards

Encodings and standards are different.

So, now you may ask, "OK, what's the difference between DOCTYPE HTML and HTML mode?"

Well, HTML and HTML5 mode are compatible. Anything you write in one will be displayed properly on a webpage that uses the other. If the page is in HTML5 mode, everything that you write in the document will be displayed on the page in plain text mode.

But the two tags are not quite equivalent. HTML5 mode lets you write certain tags and their attributes in any way you like. These tags may be displayed in any style you like, and they are guaranteed to always be displayed correctly.

HTML5 mode isn't compatible with DOCTYPE HTML, because it lacks the guarantee that the HTML tags are always displayed correctly. (In HTML5 mode, there are a number of HTML tags which may be displayed incorrectly, and they have different rules for displaying them in plain text mode than in HTML mode.)

In plain text mode, with a document in XHTML mode, you cannot have a DOCTYPE HTML tag because that would cause the HTML tags to display differently from the way they are displayed in HTML mode.

In plain text mode, with a DOCTYPE HTML tag, you cannot use HTML5 mode because that could give you inconsistent results.