For compound glyphs a font has to specify where the components of the glyph are positioned. This is usually done with s and y coordinates, but the glyf table allows using point values to align the component. This is indicated by setting the ARGS_ARE_XY_VALUES flag to false and will align a point from the current component to a point of the previous components. OpenType 1.9 has improved documentation on this feature, so it is quite clear how it should work.
In order to test if font renderers implement this feature correctly, I need a font that actually uses point values for aligning compound glyph components.
Does such a font exist?
Edit:
I have run a little script over all fonts in Google Fonts. Here is the result:
1580 fonts containing 2121337 glyphs in total were examined. 476367 of all glyphs were compound glyphs.
Number of compound glyphs using point values: 0
So at least none of the 1580 fonts on Google Font uses point values in compound glyphs. Still, there are thousands of fonts out there that are not on Google Fonts, so I am still hoping to find a font that does.