In a more general sense for a "sex sort story", the social context regarding gender can be an element. In a society where gender equality is still a struggle, a story might highlight the efforts of people to break free from gender - based limitations. It could show how both men and women are trying to redefine traditional gender norms, like in a story where men are taking on caregiving roles more often and women are entering fields like engineering in larger numbers.
If it's a story sorted by gender, then perhaps the way the story is organized around different genders is an element. For example, the story might start with male - centered events and then shift to female - centered ones. Also, the relationships between different genders in the story are important elements. In a story about a co - ed school, how boys and girls interact, compete, and cooperate can be key elements of the story.