I've come up with a updated (and more detailed) version of class and
sequence diagrams for the new widget.
I tried to incorporate some of the comments. Note that all names are
subject to change ;-)
Our now called GimpUnitEntry will be derived from GtkSpinScale and use a
subclass of GtkAdjustment to store its value including the unit
(GimpUnitAdjustment). All synchronisation and live updating of
associated UnitEntries will happen directly between their
GimpUnitAdjustments, thus completely separating everything value-related
from the gui and input. The GimpUnitEntry itself will be just
responsible for display and parsing of entered terms. See use cases and
class diagram for details.
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