go - Appending one element to nil slice increases capacity by two

Question

I have a nil slice:

var s1 []int // len(s1) == 0, cap(s1) == 0

Which I append one element to:

s2 := append(s1, 1) // len(s2) == 1, cap(s2) == 2

Why is appending one element to a nil slice increases the capacity by 2?

Printing the slices using fmt.Printf shows the following:

[] // s1
[1] // s2

I am also confused about why re-slicing s2[0:2] shows a zero which was not in the original slice nor appended to it:

[1,0] // s2[0:2]

Answer 1

Waitting for answers