1) splices are required to be made in some type of approved box, not just simply out in the open, 2) splices cannot be made in any form where it is inaccessible (i.e. hidden inside a wall), 3) the box in which the splice is made cannot be left to simply float about; it needs to be secured in place, 4) the box cannot contain more than a certain number of conductors, based on the size of the box, 5) wires entering the box need to be secured to the box by some approved type of clamp, and 6) the box must be grounded.
With due allowances for different style fittings, that's pretty much the same as is required over here in England. (Most of it is just common sense really!)
About the only major difference is that our j-boxes don't normally have built-in cable clamps, so they need to be clipped near to the box.
