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