I understand that the link is a docdb rule.

However, the CN application number in EPODOC format seems to have different numbers of digits.

Is there any document on the format rules of CN application number in EPODOC format?

We recognize that the EPODOC number format rules are as follows. https://www.epo.org/searching-for-patents/data/coverage/regular.html However, Espacenet and DOCDB CN application numbers may have different numbers of digits. - 6digits APP CN20171003156 20170104 PUB CN106587179 (A) ― 2017-04-26 https:...