The contest sexual and violent obscenity "rule" appears to limit content to a young-adult maturity level: the shorthand term PG-13 means parental guidance for age thirteen years old. Thirteen is the mean age of adult onset, physically adult-like, not emotionally adult. PG-13 for a contest term started from K.D. Wentworth's description of a comparable film content rating model.
Thirteen-year-olds are generally curious about sex and violence and have a degree of aptitude for those topics. They can possibly handle more than parents might allow, probably emotionally benefit from some exposure to sex and violence topics. They probably want to know more than they can understand and cope with, too.
The two features of PG-13 -- parental guidance and thirteen years old -- are dissonant and as well reconcilable. How much sex and violence a parent might allow a thirteen-year-old to experience can be constructed from an aggregate of public social behavior customs; that is, what a parent is socially expected to allow a child teenager. The customs' axis ranges between extremes of none, or G for general audiences, for any age child or adult according to outspoken moral authorities and anything short of unacceptable sexual and violent behavior by any entity. The mean for PG-13 is some violence and sexual content but nothing explicit or gratuitous.
Gratuitous content is simply anything unnecessary to any story movement, including violence or sexual content. If a sexual or violent piece is only necessary to plot movement, it is melodramatic and artless, though one step improved over gratuitous. If a sexual or violent piece is necessary to character movement, and emotional movement, as well as event, setting, milieu, and plot movement, then the piece is essential. However, if the piece is contrary to public social moral customs for age thirteen content, the work overall is unsuited for the contest and best submitted elsewhere.
Contrarily, explicit sexual or violence content nature is probably the substantive reconciliation consideration. Instead of an explicit description, an implied description could pass notice. An implicit description appeals to older adults though passes by younger adults. No reason to drop in obscene words when actually stronger and clearer euphemism words appeal more. For example, Motherloving child of a barrel racer. No need to explain. Dunghead. Her blossoms thrust out firm and supple and the pink of primrose. They did the two-as-one horizontal slip-and-slide. Metaphor and similar tropes euphemistically substitute implicit content for explicit content.