It is a block-level element, used to divide large block content areas; it is an inline element, suitable for wrapping small segments of text or content fragments. The specific differences are as follows: 1. Exclusively occupy a row, width and height, inner and outer margins can be set, which are often used in layout structures such as headers, sidebars, etc.; 2. Do not wrap lines, only occupy the content width, and are used for local style control such as discoloration, bolding, etc.; 3. In terms of usage scenarios, it is suitable for the layout and structure organization of the overall area, and is used for small-scale style adjustments that do not affect the overall layout; 4. When nesting, it can contain any elements, and block-level elements should not be nested inside.

To correctly set the character encoding of the HTML document to UTF-8, you need to follow three steps: 1. Add at the top of the HTML5 part; 2. Configure the response header Content-Type: text/html; charset=UTF-8, if Apache uses AddDefaultCharsetUTF-8, Nginx uses charsetutf-8; 3. Select the UTF-8 encoding format when saving HTML files in the editor. These three links are indispensable, otherwise it may lead to garbled page code and failure of special character parsing, affecting user experience and SEO effect. It is important to ensure that HTML declaration, server configuration and file saving are consistent.

To get started with HTML quickly, you only need to master a few basic tags to build a web skeleton. 1. The page structure is essential, and, which is the root element, contains meta information, and is the content display area. 2. Use the title. The higher the level, the smaller the number. Use tags to segment the text to avoid skipping the level. 3. The link uses tags and matches the href attributes, and the image uses tags and contains src and alt attributes. 4. The list is divided into unordered lists and ordered lists. Each entry is represented and must be nested in the list. 5. Beginners don’t have to force memorize all tags. It is more efficient to write and check them while you are writing. Master the structure, text, links, pictures and lists to create basic web pages.

ShadowDOM is a technology used in web component technology to create isolated DOM subtrees. 1. It allows the mount of an independent DOM structure on ordinary HTML elements, with its own styles and behaviors, and does not affect the main document; 2. Created through JavaScript, such as using the attachShadow method and setting the mode to open; 3. When used in combination with HTML, it has three major features: clear structure, style isolation and content projection (slot); 4. Notes include complex debugging, style scope control, performance overhead and framework compatibility issues. In short, ShadowDOM provides native encapsulation capabilities for building reusable and non-polluting UI components.

Image not displayed is usually caused by a wrong file path, incorrect file name or extension, HTML syntax issues, or browser cache. 1. Make sure that the src path is consistent with the actual location of the file and use the correct relative path; 2. Check whether the file name case and extension match exactly, and verify whether the image can be loaded by directly entering the URL; 3. Check whether the img tag syntax is correct, ensure that there are no redundant characters and the alt attribute value is appropriate; 4. Try to force refresh the page, clear the cache, or use incognito mode to eliminate cache interference. Troubleshooting in this order can solve most HTML image display problems.

The style placement method needs to be selected according to the scene. 1. Inline is suitable for temporary modification of single elements or dynamic JS control, such as the button color changes with operation; 2. Internal CSS is suitable for projects with few pages and simple structure, which is convenient for centralized management of styles, such as basic style settings of login pages; 3. Priority is given to reuse, maintenance and performance, and it is better to split external link CSS files for large projects.

?Youcannotnesttagsinsideanothertagbecauseit’sinvalidHTML;browsersautomaticallyclosethefirstbeforeopeningthenext,resultinginseparateparagraphs.?Instead,useinlineelementslike,,orforstylingwithinaparagraph,orblockcontainerslikeortogroupmultipleparagraph

To use JavaScript to create a secure sandbox iframe, first use the sandbox attribute of HTML to limit iframe behavior, such as prohibiting script execution, pop-up windows and form submission; secondly, by adding specific tokens such as allow-scripts to relax permissions as needed; then combine postMessage() to achieve secure cross-domain communication, while strictly verifying message sources and data; finally avoid common configuration errors, such as not verifying the source, not setting up CSP, etc., and perform security testing before going online.