I made a list about ten traits of "classic" autism (below is its translation from Polish by Google Translator):
Features of "classic" autism (regardless of IQ and functional language):
1. "Social-emotional learning disability" (resulting in, among other things, deficits in theory of mind and at least partial alexithymia),
2. Idiosyncratic processing of sensory stimuli (often very unpleasant and clearly disruptive to life), susceptibility to sensory overload and shutdowns or meltdowns,
3. Strong need for constancy and predictability, for doing things the same way,
4. Rigidity and inflexibility of behavior, thinking, and interests,
5. Lack of understanding of imaginative play, at least in early childhood,
6. Often a more or less delayed speech development or even no speech,
7. More or less prosopagnosia and difficulty recognizing people by appearance and/or voice,
8. Pragmatic language impairment (limited ability to understand figurative, implicit meanings, abstract concepts, literal thinking and interpretation, difficulties with conversation and knowledge of interpersonal communication rules,
9. Poor, absent, or inadequate facial expressions and nonverbal communication,
10. Usually clearly dominated by non-verbal thinking (e.g., visual, patterns, sounds, movements).