The set of nodes is sorted into lines indexed into activeLines.
The nodes in each line are linked together in a single linked list by the
KnuthNode.next field.
This interface is used to notify layout managers about the situation around spaces, borders
and padding just before the addArea() method is called when a part is being painted.
An instance of this class represents an unbreakable piece of content with
fixed width: for example an image, a syllable (but only if letter spacing
is constant), ...
This class resolves spaces and conditional borders and paddings by replacing the
UnresolvedListElements descendants by the right combination of KnuthElements on an element
list.