[dba-VS] Part IV: Cross-posted from dba-OT: MVVM explained - looking for English language heavy review/revision, and technical review

[Salakhetdinov Shamil]

Here is the text of
"A Simple Modern Essay About a Model, a ViewModel and a View..."
A Model lives its own (rich internal) life, it knows nothing about
its environment - what and why are "owning"/collectively sharing it,
are trying to watch/follow/guess about what is happening inside 
a Model(/how a Model's (internal) state is changing).
A Model is an ObservableObject, and therefore a Model is able to expose
a few of its properties/attributes' states to the outer world, and
the latter might "hook"/subscribe to these properties' state/values
changes via a PropertyChanged(...) generic event.
A Model also knows a few Commands it can react on. A Model's reaction
on commands could result in a (set of) PropertyChanged event(s) being 
raised...
A ViewModel knows about a Model, which it owns/collectively shares 
with other ViewModel(s).
A ViewModel is also an ObservableObject (as a Model is), and therefore 
a ViewModel is able to expose a few of its properties/attributes' 
states to the outer world, and the latter might "hook"/subscribe
to these properties' state/values changes via a PropertyChanged(...)
generic event.
(to be continued in 'Part V'...)
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Салахетдинов Шамиль