Let me know in the comments if the "side issues" title of this post is not clear after reading the last two parts below.
Diagnosing: Severity and other specifiers
Severity: For each of the two symptom areas there are descriptive guides in the DSM for rating the level of current severity based on the impact on functioning (not based on number of symptoms; this is the DSM-5 move toward a dimensional, rather than categorical, diagnosis) and whether the person requires some support (Level 1), substantial support (Level 2) or VERY substantial support (Severity: Level 3).
Do severity ratings create the spectrum? No.
“Spectrum” does not mean “varying in only one dimension (severity)” This means that the severity rating does NOT simply place you on a scale from “high functioning” or “Aspergers” to “Autistic Disorder.” People on this spectrum may have fewer RRB symptoms, or more, and differ also in the specifiers below:
Specify: With or Without accompanying Intellectual Impairment, separating intellectual disability completely from autism, as coexisting rather than coextensive conditions. Still, some people mistakingly think that social impairments are merely a function of intellectual disability.Specify: With or Without accompanying language Impairment, again making this symptom another dimension on which people can vary, independent of how they vary in severity of autistic symptoms or severity of intellectual impairment.