1, 2. Grapheme clusters are not normative in Unicode, they can be tailored for specific languages. There's a default cluster finding algorithm but it's not suitable in all cases. There's no "one size fits all" approach.
3. Forward and backward are likewise language and tailoring dependent because they depend on graphemes. There may also be application-specific tailoring such as the handling of combining marks, in some scripts "forward" and "backward" are not clearly defined.
3. Forward and backward are likewise language and tailoring dependent because they depend on graphemes. There may also be application-specific tailoring such as the handling of combining marks, in some scripts "forward" and "backward" are not clearly defined.