DOM

An inclusive ancestor is
an object or one of its is an
object or one of its siblings.

An object A is preceding an object B if A and B are in the
same tree and A comes
before B in tree order.

An object A is following an object B if A and B are in the
same tree and A comes
after B in tree order.

The first child of an object is its
first child or null if it has no children.

The last child of an object is its
last child or null if it has no children.

The previous sibling of an
object is its first preceding sibling or null if it has no preceding sibling.

The next sibling of an
object is its first following sibling or null if it has no following sibling.

The index of an object is its number of preceding siblings, or 0 if it has none.

The ordered set parser takes a string input and then runs these steps:

The ordered set serializer takes a set and returns the concatenation of set using U+0020 SPACE.