The Manipulation Routines

Once a display list is created, it may be desirable to modify it; often, because of operator input. The word "manipulation" is a rather broad word, and it encompasses two distinct areas:

Element-directed functions. This includes functions whose actions affect elements in the currently open segment:
- Adding elements to a segment. The methods discussed here are more generalized than merely re-opening a segment with 〈append〉 equal to TRUE.
- Replacing elements in a segment. After setting the element pointer to the desired value, you can exchange the contents for something different.
- Deleting elements from a segment. You can delete one or more elements from the currently open segment.
Segment-directed functions. This includes those functions whose actions relate to segments other than the currently open one, and those functions that act upon entire segments at once, or even many segments at once:
- Changing references. You can cause all segments that refer to a particular segment name, to refer to a different segment name.
- Renaming segments. You can change the name of a segment in two ways:
  Rename only a single segment.
  Simultaneously rename a segment and all references to it.
- Deleting segments. This comes in several different flavors; you can:
  Delete a specified segment from the display list.
  Delete a specified segment from the display list, as well as all references to it in all other segments.
  Delete all segments simultaneously. Of course, this also removes all references.
- Copy segments. You can copy a segment from elsewhere in the display list, or even from an entirely different display list^[17], into the currently open segment.

Following are descriptions of the above routines.

^[17]This display-list-to-display-list copying is subject to restrictions: elements with the attribute DISP_IGNORE are not copied, and references are expanded.

The Manipulation Routines

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