spilitで「|」で区切れるのって3つまでですか?

print_r(split(" |,|.", "あ い,う"));

Array (
[0] => あ
[1] => い
[2] => う
)

print_r(split(" |,|.|_", "あ い,う"));

Array (
[0] =>
[1] =>
[2] =>
[3] =>
[4] =>
[5] =>
[6] =>
)

となります