11/14/2023 0 Comments Graphical web browser definition![]() It won't stop parsing the CSS file at that point and refuse to go any further. If you use a selector that the web browser doesn't understand, it will ignore the enclosed declarations and skip ahead to the next selector. You can think of this way of modelling a document as being like a document selector model.Ĭrucially, CSS adopted the same error-handing model as HTML. Using CSS's selector vocabulary, developers can target elements with a particular tag name, class name or ID. This model is represented in the form of selectors. It has a kind of 'mental model' of how parts of HTML can be targeted for styling. Changing the single CSS file was enough.īut CSS still needs some way of understanding which parts of the HTML it should be styling. Tweaking the visual style of those 100 different pages no longer involved changing each and every one. A single CSS file could be responsible for one HTML document or it could be responsible for multiple HTML documents: 10, 20, 100 HTML pages could all reference the same style sheet. The new separation of concerns had other benefits. With the arrival of CSS, HTML could return to doing what it does best: describing the structure of a document's content. Using CSS, developers could add presentational information without having it intermingled with HTML. ![]() Håkon Wium Lie and Bert Bos joined forces to work on Cascading Style Sheets. The solution was to split structure and presentation into two different languages. HTML, which was intended for defining document structure, was looking in danger of being swamped with presentational instructions. Elements and attributes for specifying fonts sizes, colours and borders were introduced. Some of those additions were adding new semantic granularity but some had absolutely nothing to do with semantics. New elements and attributes were added to the language. In the first decade of the web's life, HTML saw an explosive growth. On the other hand, this looseness has enabled HTML to grow over time without breaking in older browsers. On the one hand, this can be quite frustrating if you're a developer trying to isolate a mistake in your HTML. Be liberal in what you accept."īrowsers are very liberal in what they accept when it comes to HTML. This kind of lax error handling is an example of a design principle called The Robustness Principle or Postel's Law: "Be conservative in what you send. The browser doesn't stop parsing the HTML as soon as it encounters an element that it doesn't understand. What's interesting here is what the browser doesn't do. It displays the content while ignoring the tags it doesn't understand. When a web browser encounters an HTML element it doesn't understand, it renders whatever is in between the opening and closing tags. That's because of the error-handling model of HTML. None of these additions introduced breaking changes. Over time, we got more form fields, more structural elements like section and article and even more media like audio, video and responsive images. But the HTML language is open to new elements being added. The first version of the HyperText Markup Language had just a handful of elements. He therefore designed it to be extensible. ![]() Berners-Lee knew that he couldn't predict how the web would be used in the future. Scientific collaboration was the first use-case for the world wide web but the project wasn't designed to be limited to that usage. The first version of the HyperText Markup Language had just a handful of elements (Image credit: )
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