What is HTML/XHTML?

What is HTML?

HTML (Hypertext Markup Language) is a relatively simple document markup language. It is not a programming language. An HTML file, usually representing 1 to 5 pages on the Web, simply contains the text content of that page, a CSS template, pictures and a few special markers that indicate different types of text such as headings.

HTML files are plain text

HTML files are written in plain text, which means they contain only letters, numbers, and some symbols (e.g. = ! + % ^). There is no inherent formatting in the plain-text format. A Web browser reads this plain-text and detects special symbols and text which affect the display, so that the final result can contain formatting.

You can view the original plain text with a simple text editor like Windows Notepad. This is how you'll see the HTML "code" as you create it. When you're learning to create Web sites it is best to work directly with the code, to make sure you fully understand how everything works. Once you become experienced, you may decide that a good visual editor (i.e. not FrontPage), which will allow you to work directly with the formatted output, could save time - but you'll still need the understanding you achieved from working with the raw HTML.

Summary 

HTML is a simple language based on text and tags.

Tags are short words or codes, inside triangle brackets. They usually occur in pairs; a closing tag has the same word as the starting tag, but begins with a / symbol (within the triangle brackets). Whatever text or tags occurs between the opening and closing tags is contained by the tags, and is affected by the meaning of the tags.

Some useful tags are H1 (marks a top-level heading), P (marks a paragraph of text), and TITLE (gives a title to the Web page).

Some tags - !DOCTYPE, HTML, HEAD, and BODY - are included in all web pages. These specify the type of the document and divide it into two sections (the heading and body), but it isn't important to completely understand these tags.

 For more detailed information - index DOT html 

What is XHTML?

 XHTML is a stricter form of HTML and as such is a subset of XML which is an extremely useful, powerful and very strict way of marking up pure data.

The headers you sometimes see along with XHTML code declare what exactly the rules are.. for instance, that <a> is an anchor. In XML you can declare your own rules.

XHTML is significantly better than HTML, as it encourages good practice. Where it doesn't allow things that HTML does, it's likely there's a good reason.. for instance not using target="_blank". These things then in turn impact on the sites accessibility, consistency, search engine performance etc etc.

Even if you don't use valid XHTML it's worth validating to Strict where you can.

That said the headers like these are more a declaration of intent, so if you do have a few errors it shouldn't matter.

It may be that you can jump into coding valid XHTML. You might however find it less frustrating starting with sloppy HTML and validating 4.01 Transitional, then 4.01 Strict, then XHTML 1.0 Transitional, then XHTML 1.0 Strict.

XHTML 1.1 is where the rules become much more stringent. This involves <?xml version="1.0" encoding="iso-8859-1"?> and xml+xhtml MIME headers which switch the browsers into strict complient mode and do not allow them to compensate for sloppy coding.. that is the page falls over with errors!

Without these headers XHTML is treated as HTML and browsers will compensate for any errors.

If you are new to validation, I'd suggest getting HTML 4.01 Strict, before worrying about serving up XHTML, but would suggest XHTML is well worth doing if you have time.

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