The horizontal metrics a font program gives one glyph, in its glyph space units.
public GlyphMetrics(double AdvanceWidth, double LeftSideBearing)
The distance from the glyph's origin to the next glyph's origin.
The distance from the glyph's origin to the left edge of its outline.
OpenType "hmtx" table. PDF widths (Widths, W) take precedence over these for positioning text (ISO 32000-2
§9.2.4, §9.6.2.1); a program's advance is the fallback when the font dictionary gives none.