A simple example of such a jump is executing any GOTO statement, but IF and DO statements are really constructed out of similar implied jumps. The sequence is maximal in the sense that adding one more statement at the beginning of the block, or one more statement at the end, will make the previous requirement false. When you examine the way program control flows, the basic blocks are the natural building blocks, so making their boundaries stand out will make the code easier to follow. However, the basic block concept should be used only as a guide, you may add additional separator lines if beneficial, or drop them. However if the statements are properly indented the indentation does the job, and there is no need for separating lines.
Similar considerations apply to nested DO loops.
It is not likely that new programs will be ported to a compiler that doesn't support longer names, so maybe it's time to forget this old restriction. Identifiers should be meaningful and describe the variable, constant, procedure, etc that they represent. Highly modular programs usually declare few variables in each procedure, and have less need for long and complicated identifiers to characterize them. Naming conventions are beneficial, because they provide programs with a sense of continuity and style. Many C programmers use the Hungarian naming convention which is highly oriented towards the computer architecture, and encodes mainly info about the variable's data type.