The relative thickness of a Typeface Stroke, expressed as a named grade within the Type Family range. The scale extends from Thin or Hairline at the lightest extreme through Light, Regular (also called Book or Roman), Medium, Semibold, Bold, Extra Bold, to Black or Heavy at the heaviest. Weight is the primary axis of variation within a type family and the most common tool for establishing typographic Hierarchy. In digital font technology, weights are often mapped to numeric values on a 1–999 scale (CSS and OpenType use 100–900 in increments of 100 by convention, with 400 = Regular and 700 = Bold).