The prefix of Element for JS returns the namespace prefix.
prefix = element.prefix
attachShadow
classList
className
closest
getAttribute
getAttributeNames
getAttributeNS
hasAttribute
hasAttributeNS
hasAttributes
id
innerHTML
insertAdjacentHTML
localName
matches
namespaceURI
outerHTML
removeAttribute
removeAttributeNS
setAttribute
setAttributeNS
shadowRoot
slot
tagName
toggleAttribute
Web Hypertext Application Technology Working Group (WHATWG)
