Yes I see it there:
Maintaining legal status
Spouses and common law partners of Canadian citizens and permanent residents in Canada who wish to apply for permanent resident status are required to have legal immigration status in order to qualify under the Spouse or Common-law partner in Canada class.
Important information: Applicants who wish to be able to continue to work and study in Canada must submit an application for extension before the work or study permit expires.
I know I've read on here of many people applying within Canada without status. I think it's one of those rules they don't really enforce, but I really don't know, someone else will hopefully answer.
Another strange thing I noticed is, in the section on how to validate your COPR if you live in Canada, the website tells you that you must leave Canada then enter in order to validate it, but you have to show proof of legal status. If you leave Canada why on earth would you need legal status to validate the COPR? Makes no sense.
http://www.cic.gc.ca/english/helpcentre/answer.asp?q=748&t=22
Basically if you go by the website, no one in Canada illegally can get a PR, but the reality is that is not the case.