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