In Poland we have three levels of disability: mild, moderate, severe. Mild may be more close to normal functioning in life, moderate closed rather to severe than to full health and severe means that someone is incapable of independent existence. I was diagnosed with moderate level. I can buy many products (like food and drinks) on my own, without help of others, go to the doctor on my own without support, but I am very poor at job market and have no close relationships. I am also significantly poor in caring about household, in large part because of "obsessions" and fears about infection. I was very good in school. I am moderate-functioning, not high-functioning. I could name myself as "smart idiot" (but I, of course, do not want or try to name anyone "idiot") - this phrase (in Polish "sprytny idiota") was once used by my father to describe me. "Idiotism" is an old name of really serious (most serious) form of intellectual developent disorder. I am "like small child" in some areas. I am very severely bizarre in terms of my thought content.
I think that not only ASD may be described as "high, moderate or low functioning", but also other mental disorders, especially those which for me are different sorts of autism and PDD, like "social" NVLD or SCD. I think that people with social inadequacy and peculiarity have to be grouped in one subcategory of developmental disabilities which would include Kanner's syndrome, SCD, NVLD with social problems, some cases of schizo disorders etc.