expandBack abstract method
Expands the current range with the preceding count characters.
Expands the current range to include the last count characters
preceding the current range, or as many as are available if
there are fewer than count characters preceding the current range.
The count must not be negative.
If it is zero, the range does not change.
Returns true if there are at least count characters preceding
the current range, and false if not.
Implementation
bool expandBack([int count = 1]);