expandUntil abstract method
Expands the range to include characters until the next
If there is an occurrence of
target in the characters following
the current range, the end of the the range is moved to just before
the first such occurrence.
If there is no such occurrence of
target, the end of the range is
moved to the end of source.
true if there is an occurrence of
false if not.
bool expandUntil(Characters target);