For the first time, Facebook spells out what it forbids

For the first time, Facebook is making public its detailed guidelines for determining what it will and won't allow on its service.

The guidelines, due out Tuesday, are an updated and public version of Facebook's internal "community standards."

The company says the 27-page document mirrors the rules its reviewers use to decide whether posts run afoul of prohibitions against harassment, violent threats, explicit sexuality and other forbidden categories.

Facebook has previously shied away from providing this level of detail about its rules, which can get rather complex. Photographs of bare breasts, for instance, are allowed in some cases, such as breastfeeding or artistic depictions in paintings, but not in others.