Перемещение по дереву DOM, создание и удаление тэгов и атрибутов

parentNode
childNodes
previousSibling
nextSibling
children
firstChild
lastChild

querySelector
querySelectorAll

appendChild
insertBefore(newNode, beforeNode)
replaceChild(newNode, oldNode)
removeNode
cloneNode(true)

getElementById
getElementsByTagName
getElementsByName - для радиокнопок
getElementsByClassName("username current");

getAttribute
setAttribute
removeAttribute

Also note that, according to HTML5, custom attributes should be prepended with "data-" in order to validate.

createElement
createTextNode
createComment
createDocumentFragment

element.normalize
textNode.splitText