Several of the options interact with the rule menu, since one of the important applications of the line editor is to define transitions. The basic operation is the insertion of a definition, but marking it for future reference is an important secondary operation. Marking may distinguish between transitions already settled upon and those yet to be defined; it also serves to protect the designated transitions from the random number generator.
In referring to the ``transition under the cursor,'' a neighborhood of the appropriate length is taken from the line just above the cursor, cyclically wrapped if the cursor is near the margin. To make sense, the cursor must be in the second row or lower.