Salam and Hi,
I just tried to use the RSB/LSB anchors in an Arabic glyph, the one in the picture
I am using two parts here, the sad-ar.init (i did put the LSB anchor inside it to the far left) and the join component (And i did put the RSB anchor inside it to the far right of it) I wanted to do this so save my self time re-assigning these RSB/LSB values for all sad-ar instances (As a test) whenever a change in design/width happen (like 200 times per day) But the result was very unexpected (A real bug or a missing implementation!) The RSB anchor on the right side of the join component was actually pushing the sad-ar.medi glyph from the LEFT SIDE … not the right side!
More than that, the change was not reflected at all in the exported font, nor in the preview panel inside glyphs…
Not only CJK fonts need this… Arabic fonts need it too… And they need it soon
May Allah guide you and bless you…