Atribut xmlnsAbout xmlns, same thing. https://www.w3.org/TR/html5/dom.html#global-attributes immediately following the quotation issue, it is said:Note: In HTML, the xmlns attribute has absolutely no effect. It is
basically a talisman. It is allowed merely to make migration to and
from XHTML mildly easier.Note: HTML, xmlns Atribut has no effect. It's just
Talisman. It only makes it easier to make a change and make it easier.
XHTML documents.We're not going to need HTML. It can certainly be used for HTML elements, but it doesn't make sense, because for all HTML structures, the document already has predetermined meanings of the name space, the list of which is on the question, and no one will change them to other meanings. In other words, the following examples are tantamount to:<html xmlns="http://www.w3.org/1999/xhtml">
<html>
There you go. <html xmlns="что-то своё"> It's not gonna work, because xmlns is just ignored, and html will still be in the area of the name. http://www.w3.org/1999/xhtml "as stated above.About the name spaceIn analogous to the names of classes, packages, etc. from the programming languages, the language of the name distinguishes one element from another when they have the same name but belong to different areas of the name. Where can this happen at HTML? For example, when we use svg in html:<svg>
<a xlink:href="/"><text x="0" y="20" fill="green">Ссылка в SVG</text></a>
</svg>
<a href="/">Ссылка в HTML</a>
And we had to change the size of the svg reference. Just write in style. a { font-size: 1.5em } It won't work, as this rule will also apply to the usual reference. This is where the CSS is able to work with the names spaces. To this end, the CSS will carry out such actions:(1) Using the key word @namespace, we're referring to the name of the "supply" of the space of the names we're dealing with:@namespace svg url(http://www.w3.org/2000/svg);
Note: The SVG space address is taken from the specification and another name can be used instead of svg.(2) Now, svg can be directly accessed to the mark. <a>which is located in <svg></svg>with special CSS synthesis:svg|a { font-size: 1.5em; }
TotalI don't need any HTML.The specification for us identified the names of the domains of the names for specific HTML, XML, SVG and their elements.For CSS to access a specific element using the name space, a form should be used. namespace|css-selector, prescribing the name for the space by @namespace.