Where does the '' in the source code of the website (picture) come from?_html/css_WEB-ITnose

itemref is an attribute in Microdata that is used to disperse content in associated pages. Its main purpose is to enable elements that do not belong to the current item scope to become part of the object, thereby realizing remote reference. The usage methods include: 1. Add item scope and unique id to the main object; 2. Use itemref to refer to the id of other elements on the main object; 3. The referenced element must have itemprop and the id is consistent with the itemref list. Applicable scenarios include layout restrictions, multiplexing structures, CMS systems, etc. Notes include: It can only be used for elements with item scope, the target element must be the same page, the id must be unique, not all tools support itemref, it is recommended to make

The placeholder property is an auxiliary function in HTML forms for input box prompts. It displays light text when the input box is empty, and it will automatically disappear after the user starts input. The correct way to use it is to use it as a supplementary description rather than replace label tags. The specific steps are: 1. Use label and placeholder at the same time, such as username: 2. Avoid labeling required items or providing key information with placeholder; 3. Control the length of the prompt text to keep it simple; 4. Adjust the style through CSS to ensure compatibility; 5. Applicable to input scenarios with clear formats such as email, search boxes, etc., and password boxes should be used with caution.

The track element is a tag in HTML5 that is used to add text tracks to videos. It supports subtitles, titles, descriptions, chapters, and metadata, and is usually made using WebVTT format files. 1. When using it, you need to add and specify properties such as src, kind, srclang, label, etc. 2. The WebVTT file format must start with WEBVTT and include timestamps and contents. 3. Mainstream browsers support track but limited style control. 4. Multiple tracks can be added to achieve multilingual support. Correct use of track can improve video accessibility and user experience.

TobuildarichtexteditorusingHTML’scontenteditableattribute,startbymakinganelementeditablewithcontenteditable="true",thenhandleformattingwithJavaScriptviaexecCommandorDOMmanipulation.1.Usecontenteditableonelementslikeorfordirectediting.2.Hand

Common HTML event attributes include onload, onchange, onsubmit, onmouseout, onkeydown and onkeyup; onclick is used to respond to click behavior, and it is recommended to achieve interaction through function calls or JS binding; onmouseover and onmouseout are often used for hovering effects; it is recommended to use addEventListener to achieve event binding for maintenance and extension.

details and summary tags can achieve folding and expansion effects without JavaScript. 1. Details is used as a container, and the content is hidden by default; 2. summary is used as the title to open and close; 3. You can customize the style through CSS, such as removing the default arrows, setting backgrounds and padding; 4. Applicable to FAQ, setting panels and other scenarios; 5. Pay attention to browser compatibility and structural correctness, and summary must be placed inside details.

Formaaction is an attribute in an HTML form that specifies the independent submission address of a specific submission button, which overrides the form's default action attribute. 1. It allows setting different submission paths for different buttons, such as "Save" and "Preview". 2. When using it, it is directly added to the button of type="submit", and the syntax is format="url". 3. It can be used in combination with other attributes such as formmethod, formctype, and formtarget to achieve flexible submission behavior. 4. The priority of this property is higher than the action of the form, and the path can be a relative or absolute path. 5. Commonly used for many

When using target="_blank", rel="noopener" must be added at the same time to prevent security vulnerabilities. The reason is that the new page can control the original page through window.opener, causing phishing or redirecting attacks. The correct way to write it is:. If you need to affect SEO, you can add nofollow: rel="noopenernofollow". Scenarios that need special attention include: 1. User-submitted links; 2. Content generated by third-party plug-ins or CMS; 3. Advertising or cooperative links. In addition, target="_blank" should be used with caution,