version
A version with an arbitrary number of components.
The first three components have names that can be used as fields: major,
minor, patch. All following components do not have names.
The list of components is semantically extended by an infinite list of
zeros. This means that, for example, 0.8 is the same as 0.8.0. As a
special case, the empty version (that has no components at all) is the same
as 0, 0.0, 0.0.0, and so on.
You can convert a version to an array of explicitly given components using
the array constructor.
构造函数参数参数是传给函数的输入，写在函数名后的括号中。
Creates a new version.
It can have any number of components (even zero).
#version() \
#version(1) \
#version(1, 2, 3, 4) \
#version((1, 2, 3, 4)) \
#version((1, 2), 3)
定义定义这些函数和类型带有附属定义。要访问这种定义，请先写上函数或类型的名称，再加上定义的名称，并用句点在中间分隔。
at
Retrieves a component of a version.
The returned integer is always non-negative. Returns 0 if the version
isn't specified to the necessary length.
index
The index at which to retrieve the component. If negative, indexes from the back of the explicitly given components.