Definion of 'for' statement in the manual

[Niccolo Medici <niccolomedici@...>]

The reference for Lua 5.2 says:

  """
  More precisely, a 'for' statement like

    for v = e1, e2, e3 do block end

  is equivalent to the code:

    do
      local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
      if not (var and limit and step) then error() end
      while (step > 0 and var <= limit) or (step <= 0 and var >= limit) do
        local v = var
        block
        var = var + step
      end
    end
  """

Whereas the reference for Lua 5.3 says it's equivalent to:

  """
  do
    local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
    if not (var and limit and step) then error() end
    var = var - step
    while true do
      var = var + step
      if (step >= 0 and var > limit) or (step < 0 and var < limit) then
        break
      end
      local v = var
      block
    end
  end
  """

My question:

Why does Lua 5.3's reference does "var = var - step" instead of simply
moving the "var = var + step" after "block" (as in Lua 5.2)?