Now that we have seen how web pages get from the server to the browser, we should turn to how they are actually made. That is what we're going to be spending most of the course learning about.
Web pages are constructed using three main technologies, each of which plays a different role in the creation of the pages.
First is HTML, the HyperText Markup Language. HTML is used to describe the content of pages and its usually what people are talking about when they mention “a web page”. In HTML, we will express things like “this is a paragraph” or “this is an important word”. We aren't concerned in HTML how those things look. We will cover the basics of HTML further in the unit Markup and HTML.
Since HTML describes only the content itself, we need some other tool to make it look a certain way: that is CSS, Cascading Style Sheets. We can use CSS to suggest appearances for the pieces of content we have created in HTML. For example, we can express ideas like “all paragraphs should have this font size” with CSS. We will introduce CSS in the unit Stylesheets.
These three technologies form the basis of what we know as “web pages”, and the basis for this course.
Why separate Content, Appearance, and Behaviour?
At this point, it might not be obvious why we need three different pieces of technology to create web pages. Hopefully, the distinct uses of these three things will become obvious as the course goes on. But for now, we can at least introduce the broad motivation.
As we actually start working with these technologies, you will hopefully convince yourself that these things are true, and that there are other reasons to keep these concepts separate.