There are three (and only three) places where types can be explicitly annotated in Hack.

# Function and Method Returns

# Function and Method Parameters

# Class Properties

## Abstract class constants

In addition to typing properties with their datatype, you can also declare constants abstract in an abstract class

There are three (and only three) places where types can be explicitly annotated in Hack.

# Function and Method Returns

# Function and Method Parameters

# Class Properties

## Abstract final classes

## Abstract class constants

In addition to typing properties with their datatype, you can also declare constants abstract in an abstract class

Make sure we document abstract final classes
Make sure we document abstract final classes

Not sure if it is currently in the right place or we need to separate it out
to some other or new section of the docs, but we will see.
