It is in the site guidelines. If you ever need to refer to it, there is a site guidelines button at the upper right side underneath the Eurobricks banner.
LEGO Ideas: If you have a great MOC, that is also a LEGO Ideas project, you may present it on EB as you would any MOC, with a single link to the Ideas entry. Make the title about the MOC, not the Ideas business; don't be too shouty, and it is likely to be tolerated. You need to be thinking: 'I want people on EB to see my MOC and comment on it. If they like it, perhaps they'll support it on LEGO Ideas', rather than: 'I want Ideas support! If I post it on EB, perhaps more people will vote!.