The main assembly,
ComposerCore, is not dependent to any packages and only relies on the API provided by net-standard 2. Any code that required additional dependencies is separated into additional projects/packages (like CompoerCore.Aop)
ComposerCore is built on net-standard 2, so it can be run on any runtime that supports it. This includes .NET Core 2.0+ and .NET Framework 4.7.1+.
ComposerCore is meant to be more than just IoC/DI. Although very similar in features, it's rather built to promote and facilitate designing software that is formed from well-defined, replaceable or composable parts. What happens in action is very similar to IoC/DI containers with Auto Wiring turned on, and there's little difference visible (if any).
It's a relatively-popular design pattern used in Object Oriented programming. The basic ideas behind the pattern is best described by Martin Fowler here: https://martinfowler.com/articles/injection.html
Actually, from version 1.4+ they are not. You can disable attribute checking using a setting in Configuration, but it's not recommended. Because the attributes are used to differentiate components and contracts from regular classes and interfaces, and make it explicit both for the coder and the reader. It's somewhat similar to type checking in a static language like C#. Read more about it in Attributes pages.
Both.
It's recommended to use property-injection, but ComposerCore can also identify constructor arguments and inject them as well, when creating a component instance. You can even use them together at the same time, having both constructor arguments and injection properties on a single component at the same time.
Yes.
Also it might be a sign that you have a flaw in your design, Composer can handle cyclic dependencies between components and will not throw
StackOverflowExceptionor anything when there's a loop instantiating the components. Although this is only true when you're using property injection. For constructor injection, there's no way of instantiating an object with arguments that will be created later!
The ComposerCore itself is independent of any other library except the net-standard version 2. Many APIs are not present in the net-standard yet. To keep the core composition functionality independent of any external libraries and not enforcing any additional references for usages, we've determined to separate projects/packages that need additional references. As an example, ComposerCore.Aop is dependent to Reflection.Emit.