Accessibility Levels

When access is allowed to a member, it said to be accessible. Otherwise, it is inaccessible. Use the access modifiers, public, protected, internal, or private, to specify one of the following declared accessibilities for members.

Declared accessibility	Meaning
public	Access is not restricted.
protected	Access is limited to the containing class or types derived from the containing class.
internal	Access is limited to the current assembly.
protected internal	Access is limited to the current assembly or types derived from the containing class.
private	Access is limited to the containing type.

Only one access modifier is allowed for a member or type, except for the protected internal combination.
Access modifiers are not allowed on namespaces. Namespaces have no access restrictions.
Depending on the context in which a member declaration takes place, only certain declared accessibilities are permitted. If no access modifier is specified in a member declaration, a default accessibility is used.
Top-level types, which are not nested into other types, can only have internal or public accessibility. The default accessibility for these types is internal.
Nested types, which are members of other types, can have declared accessibilities as indicated in the following table.

Members of	Default member accessibility	Allowed declared accessibility of the member
enum	public	None
class	private	publicprotected internal private protected internal
interface	public	None
struct	private	publicinternal private

The accessibility of a nested type depends on its accessibility domain, which is determined by both the declared accessibility of the member and the accessibility domain of the immediately containing type. However, the accessibility domain of a nested type cannot exceed that of the containing type.