CairoFontExtents.Descent (gb.cairo)
Property Read Descent As Float
Returns the distance that the font extends below the baseline.
This value is positive for typical fonts that include portions below the baseline.
Note that this is not always exactly equal to the maximum of the extents of all the glyphs in the font, but rather is picked to express the font designer's intent as to how the the font should align with elements below it.