hhea: Horizontal Header

The horizontal header table contains global horizontal writing metrics which apply to all glyphs in the font.

Requirements

The advanceWidthMax, minLeftSideBearing, and minRightSideBearing fields must reflect the actual data in 'glyf' and 'hmtx'. Glyphs with no contours should be ignored for the purposes of these calculations.
The values of caretSlopeRise and caretSlopeRun should agree with the italicAngle in the 'post' table.

Recommendations

The Ascender, Descender, and LineGap fields are typographic values, not strict calculations. The TTF specification contains additional information on baseline-to-baseline distances in the chapter "Recommendations for Windows Fonts".