In digital fonts, curves are defined by at least two end points (also called on-curve points or nodes) and one or more off-curve points (also called handles), which control the shape and tension of the curve.

Extrema points are the highest, lowest, leftmost, or rightmost points on a curve. These can be recognised by their associated handles, which align strictly horizontally or vertically.

Hints can only attach to extrema points. For proper rasterization (conversion of vector shapes into pixels), it is therefore essential to ensure these points are present and correctly placed.

NOTE

Since PostScript hinting doesn’t apply to diagonal stems, it is debated whether vertical extrema are necessary in italic shapes.