For some, a chapter on constants, presets and parameters will seem drier than the Namib desert, but I've long found these to be a rich and fertile way in to the ideas and mechanisms we'll be unpacking in detail in later chapters. Far from being a desert, this part of the spec bustles with life.
The foundation is laid with a set of custom data types. The beacon chain specification is executable in Python; the data types defined at the top of the spec represent the fundamental quantities that will reappear frequently.
Then – with constants, presets, and parameters – we will examine the numbers that define and constrain the behaviour of the chain. Each of these quantities tells a story. Each parameter encapsulates an insight, or a mechanism, or a compromise. Why is it here? How has it changed over time? Where does its value come from?