Often the help to be provided when the student presses the HELP key is a brief statement or small drawing which will fit easily on the “page” or screen display which the student is viewing. When this is the case, such help can be added to the screen by means of a -help- command if an “inhibit erase” is used to prevent the current display from disappearing.
A better way is to use a -helpop- command. The statement “helpop hint” specifies that unit “hint” should be done when the student presses the HELP key, without erasing the screen. After going through unit “hint”, TUTOR returns to the point in the lesson where you were waiting for the student to press a key. This could be a -pause- statement, the end of a unit (where you were waiting for the student to press NEXT to
proceed to the next main unit), or an -arrow- command where the student was entering a response. The fact that TUTOR returns to the waiting point is an additional advantage of -helpop- over the -help- command, since return from an ordinary help sequence goes all the way to the beginning of the base unit, rather than to the waiting point. (Since the original display is still on the screen when -helpop- is used, there is no need to redo the base unit to restore the screen display.) No -endcommand is needed in a -helpop- unit, unlike a -help- unit.
The set of on-page commands includes -helpop-, -helplop- (associated with the HELP1 or shift-HELP key), -dataop-, -datalop- (for the DATA1 key), -labop-, and -lablop- (LAB1 key). The -termop- command mentioned earlier permits TERM-associated displays “on the page”.
For moving among main units there are the commands -nextop-, -nextlop-, -backop-, and -backopl-. These are just like -next-, -nextl-, -back-, and -backl-, except that the screen is not erased when proceeding to the named unit. These features can be mixed in one unit. If a unit contains a -nextop- command and a -back- command, the screen will not be erased when NEXT is pressed, but it will be erased if BACK is pressed.