This command produces a new list from list by inserting all of the element arguments just before the index'th element of list. Each element argument will become a separate element of the new list. If index is less than or equal to zero, then the new elements are inserted at the beginning of the list, and if index is greater or equal to the length of list, it is as if it was end. As with string index, the index value supports both simple index arithmetic and end-relative indexing.
Subject to the restrictions that indices must refer to locations inside the list and that the elements will always be inserted in order, insertions are done so that when index is start-relative, the first element will be at that index in the resulting list, and when index is end-relative, the last element will be at that index in the resulting list.
Putting some values into a list, first indexing from the start and then indexing from the end, and then chaining them together:
set oldList {the fox jumps over the dog}
set midList [linsert $oldList 1 quick]
set newList [linsert $midList end-1 lazy]
# The old lists still exist though...
set newerList [linsert [linsert $oldList end-1 quick] 1 lazy]