Here's a snipet of code from another post here on the forums..(Thanks CAB)
((= (cdr (assoc 0 (entget ename))) "ARC")
(prompt "\nObject is an Arc, Try again.")
Is there any sort of list out there that breakdowns what each "assoc" relates too? (i.e. in the above example, assoc 0 relates to the object type being an "arc") I know you are able to extract such things as start and end or center point from the "assoc" values, maybe someone can help expand on this?