the problem with only digits is that sometimes the uploaders have not idea how many parts an author may release a chapter as
you may have 4.1, 4.2, 4.3, ... 4.10, 4.11, ... 4.100 in that order
however people may understandably get confused with 4.100 > 4.2
as a number 42/10=4.2 > 4.100
it...