Fence system with variable position rail

A modular fence system. The system includes fence planks designed for insertion into open channels of upper and lower fence rails. The fence rails are supported in a horizontal orientation between intermittent fence posts, with the open channels facing toward a vertical direction and with the fence planks extending vertically between the rails and into the channels. The planks preferably include resilient protrusions at their upper ends. The protrusions of the planks are designed to fit into internal passages formed in the open channels of the upper fence rail, into engagement with ledges defining the passages, to inhibit inadvertent removal of the planks from the upper rail. The fence rails can also be used in a different way and in a different position, in which the open channels face toward a horizontal direction, with an elongate cap coupled to the rail to cover the open channel. Plank members are coupled to the cap such that the cap resides between the plank members and the rail.