FILL,[<n1>],[<n2>],[<nr>]

generates a line of nodes between two existing nodes (by interpolation); <nr> = number of nodes to be filled-in between <n1> and <n2>; if <nr> is not specified, default value will be used: <nr> = <n2>-<n1>-1; if <n1> and <n2> are not specified, these will be set to the latest two consecutively defined nodes.