<base>

The Document Base URL element. The <base> HTML element specifies the base URL to use for all relative URLs in a document. There can be only one <base> element in a document.

A document's used base URL can be accessed by scripts with Node.baseURI. If the document has no <base> elements, then baseURI defaults to location.href. vueRouter4 中 createWebHistory normalizeBase(base)需要对 base 进行格式化，就用到了 <base> 标签