Glyphs is not grouping anchors in GPOS

Glyphs
1

this is inside abvm
pos base [knTTHUU] <anchor 301 674> mark @mark_top;
pos base [knDDUU] <anchor 389 674> mark @mark_top;
pos base [knDDHUU] <anchor 389 674> mark @mark_top;
pos base [knNNUU] <anchor 387 674> mark @mark_top;
pos base [knTUU] <anchor 290 674> mark @mark_top;
pos base [knTHUU] <anchor 365 674> mark @mark_top;
pos base [knDUU] <anchor 365 674> mark @mark_top;
pos base [knDHUU] <anchor 365 674> mark @mark_top;

Glyphsapp can group the knDDUU and knDDHUU, knDUU and knDHUU, since they have same anchor at same position,

	pos base [knDDUU knDDHUU ]  <anchor 389 674> mark @mark_top; 
	pos base [knDUU knDHUU ]  <anchor 365 674> mark @mark_top;

same needs to happen in definition of markclass.

2

I check that but it should not make a difference in the resulting binary.

3

I have not looked in the final font file.

But in the features.fea it’s not grouped.

If this true in final file, there is an opportunity to shrink the file size

4

In most fonts, most marks have unique positions and the saving potential is very limited.