This is a very common short-cut found in shader languages for swizzling operations. In short:

v.xxyz <=> (v.x, v.x, v.y, v.z)
v.s00112233 <=> (v[0], v[0], v[1], v[1], v[2], v[2], v[3], v[3])

For a single variable like this, the notation is a little contrived, but imagine that 'v' above is replaced by a fairly complicated expression.