### glyphAdvanceWidths

The optional "glyphAdvanceWidths" structure describes the advance width of each glyph. The advance width is defined as the width of a glyph as measured from its origin to the origin of the next glyph on the line. In text fonts for many languages, glyphs normally have positive left and right side-bearings, i.e. space to either side of the glyph, so that a string of glyphs will show the expected letter spacing. The advance width includes these side-bearing values. If a glyph's path protrudes beyond the width defined for the glyph in the font, however, these protrusions to the left or the right – which can be termed negative side-bearings – are not included in the advance width.

In SMuFL fonts, glyphs typically have zero left and right side-bearings, and some glyphs may have negative side-bearings. For example, stemSulPonticello has a very narrow width, and large negative side-bearings to accommodate the sul ponticello sign that is centered on the stem.

Values in the "glyphAdvanceWidths" structure are expressed as a single value in staff spaces, to any required degree of precision.

Below is an excerpt from a dummy font metadata file for Bravura, with a section of the "glyphAdvanceWidths" structure filled in:

    {
    ...
      "glyphAdvanceWidths":
      {
        "analyticsNebenstimme": 2.836,
        "figbass9": 0.944,
        "pictBeaterSoftBassDrumDown": 1.28,
        "wiggleCircularEnd": 0.648,
      ...
      }
    }

For each glyph, the "glyphAdvanceWidths" structure provides the glyph’s name and its advance width.