Denmark is Forever?

Today I called to the Citizen Service Centre in Aarhus to apply for my CPR number (kind of a PPS equivalent). I took a ticket, joined the queue and within two minutes I was called - great, as you usually end up waiting for ages in this type of queuing system (and from hearing stories about applying for the PPS number). I had already applied for my Certificate of Registration and I handed this along with my passport to the lady at the desk. She gave me a form I had to fill out while she went off to photocopy my documents. The form was written in English and Danish, and she said if you have any questions about the form, just ask. So I began filling in my name, address etc and then I stopped at a question. Hmmm...well, I'm not sure about this one. And then she asked, 'oh do you need help?', and I said, 'well, it asks 'what is the estimated duration of your stay in Denmark', and I said, 'well, I have moved here to live and work....so....' and she answered...'forever. You can just write 'forever''. So as I filled in forever in capital letters, it made me think that there is no answer to this question. I guess many people write down 'one year' if they are here to study or take a gap year from home, but for others who move to Denmark, we never know how long we will stay (or maybe you can't actually leave...I should investigate that).