Comments by Tonven (Top 4 by date)

And how to show this Tooltip for both fields, the property I changed and the property from what it depends?( in your example for weith and heith so make red both fields on propertychange of ONLY one?

As I said, I work with DataGrid, update it from another textbox. And I need to work not only with properties, but with complex errors, and I should see mistakes when property changes.

I read your article, but I have a bit another problem , when I need to have a rule, which involves several properties(for example, if u tell that u was born in London but not in England i need to display exception). I can do this, but only at the start of application, or when u sort DataGrid, because all this iitems are stored in DG.