Imagine you have a watch named 'e' whose value is an object of type
PropertyChangeEvent at a moment. The PropertyChangeEvent has a field named
'newValue' of type Object. At the moment, value of the field 'newValue' is an
object of type Point:

e.newValue = <some Point>

Furthermore, you want to permanently watch value of field 'x' of this Point.
Currently it is possible to create a "fixed watch" from 'e.newValue', expand the
node that represent this "fixed watch" and watch value of its field 'x'.

Enhancement: Allow to declare a "partially fixed watch" by entering a special
expression as the value of property 'Name of variable' of a watch, e.g. by
entering expression

    #(e.newValue).x
you would watch a (non-fixed) value of field 'x' of a fixed instance (referred
to by the current value of 'e.newValue').