Why can my instance initializer block reference a field before it is declared?

Question

My understanding is that you cannot reference a variable before it has been declared, and that all code (including instance initializers) that is within the body of a class,

Answer 1

From docs:

8.3.2.3. Restrictions on the use of Fields during Initialization

The declaration of a member needs to appear textually before it is used only if the member is an instance (respectively static) field of a class or interface C and all of the following conditions hold:

• The usage occurs in an instance (respectively static) variable initializer of C or in an instance (respectively static) initializer
  of C.

• The usage is not on the left hand side of an assignment.

• The usage is via a simple name.

• C is the innermost class or interface enclosing the usage.

It is a compile-time error if any of the four requirements above are not met

In this case, the usage is on the left hand side of the assignment, so it is not a compile-time error.