moveNext abstract method
Moves the range to be the next
count characters after the current range.
The new range starts and the end of the current range and includes
count characters, or as many as available if there
are fewer than
count characters following the current range.
count must not be negative.
If it is zero, the call has the same effect as collapseToEnd.
true if there were
count following characters
false if not.
@override bool moveNext([int count = 1]);