How many categories are there when the attribute is "onreset"?
CREATE TABLE "common_w3_c_events" (
  "category" text,
  "type" text,
  "attribute" text,
  "description" text,
  "bubbles" text,
  "cancelable" text
);
SELECT COUNT("category") FROM "common_w3_c_events" WHERE "attribute"='onreset';