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A web engine, also known as a browser engine or layout engine, is a core component of web browsers responsible for rendering web pages. It interprets HTML, CSS, JavaScript, and other web technologies to display content accurately and interactively. The web engine's primary function is to parse HTML documents, apply styling with CSS, and execute scripts with JavaScript, ultimately rendering the content on the user's screen.
Here's how a web engine typically works:
Parsing HTML: The web engine starts by parsing the HTML document received from the web server. It breaks down the HTML code into a structured tree-like data structure known as the Document Object Model (DOM). The DOM represents the logical structure of the document, including elements, attributes, and their relationships.
Applying CSS: Once the HTML parsing is complete, the web engine proceeds to apply styles using CSS (Cascading Style Sheets). It matches CSS rules to the corresponding elements in the DOM, calculating the final styles for each element. This process, known as style computation or styling, determines the visual appearance of the web page, including layout, colors, fonts, and other stylistic properties.
Layout and Rendering: With the HTML parsed and CSS styles applied, the web engine performs layout and rendering to display the content on the user's screen. It calculates the position, size, and arrangement of each element based on its styling and relationships with other elements. This process, known as rendering or painting, involves generating a visual representation of the web page, including text, images, and other media.
Executing JavaScript: In addition to HTML and CSS, web pages often include client-side scripts written in JavaScript. The web engine executes these scripts to add interactivity and dynamic behavior to the page. JavaScript execution may involve manipulating the DOM, handling user interactions, making network requests, and updating the page content dynamically.
Handling Events and User Input: As the user interacts with the web page, the web engine handles various events such as clicks, scrolls, keyboard input, and form submissions. It responds to these events by updating the DOM, executing JavaScript event handlers, and triggering appropriate actions or behaviors.