Base class for data associated with a RenderObject by its parent.
Some render objects wish to store data on their children, such as their
input parameters to the parent's layout algorithm or their position relative
to other children.
The hash code for this object. [...]
A representation of the runtime type of the object.
Called when the RenderObject is removed from the tree.
Returns a string representation of this object.
Invoked when a non-existent method or property is accessed. [...]