moveBack method Null safety
- [int count = 1]
Moves the range to be the last
count characters before the current
The new range ends at the start of the current range and includes
count characters, or as many as available if there
are fewer than
count characters preceding the current range.
count must not be negative.
If it is zero, the call has the same effect as collapseToStart.
true if there were
count preceding characters
false if not.
bool moveBack([int count = 1]);