I’m looking at the PUA Vertical Metrics Marker characters U+F132 and U+F133 in some of the SIL Fonts (Gentium Plus Regular v5.000, Charis SIL Regular v5.000) and they are SO useful in diagnosing how applications handle vertical metrics.The Baseline, xHeight, and CapHeight are faithfully represented except …
What do the top-most and bottom-most horizontal lines represent? They’re not the Asc/Descent triplets, and I can’t see a relationship to any of the vertical metrics in the font.
Is there a document that describes the design of these glyphs?
Alternately, is there another place I should be looking for code points that show the Asc/Descent triplets (before I go off and design my own)?