Ok, seems I found my answer in debasidas' first link. Seems you have to specify values when using RANGE. If one uses HASH then you don't need to specify values. The quote below explains.
CREATE TABLE orders_hash (
id INT AUTO_INCREMENT PRIMARY KEY,
) ENGINE = MYISAM
PARTITION BY HASH(id)
MySQL determines which partition stores rows that are inserted into the orders_hash table using the modulus of the id value and the number of partitions (4). Internally, the partitions are numbered 0 to 3; this means that order #10203 is stored in partition #3, because 10203 mod 4 equals 3 (that is, dividing 10203 by 4 leaves a remainder of 3).
Furthermore, if one uses KEY and doesn't specify any columns (ie 'PARTITION BY KEY()') then the PRIMARY KEY of the table is used.