Clarify dependency property - it's still a mystery to me

I still have no idea why I would use a dependency property or what it does that a normal property would not do. Needs an example and illustration of the difference in appearance or behaviour that would result.

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* ID: 73a26290-f551-b7c3-3677-426ea3fb39d9
* Version Independent ID: 8e6e4275-ed51-8425-7d6b-ee4a4b1c3fba
* Content: [Dependency properties overview - WPF .NET Framework](https://docs.microsoft.com/en-us/dotnet/desktop/wpf/advanced/dependency-properties-overview?view=netframeworkdesktop-4.8)
* Content Source: [dotnet-desktop-guide/framework/wpf/advanced/dependency-properties-overview.md](https://github.com/dotnet/docs-desktop/blob/master/dotnet-desktop-guide/framework/wpf/advanced/dependency-properties-overview.md)
* Product: **dotnet-framework**
* Technology: **dotnet-wpf**
* GitHub Login: @adegeo
* Microsoft Alias: **adegeo**