MarkToBase clarification?

[Ken Lunde]

All,

For those who are familiar with MarkToBase, the following was sent to me from a friend at Fontworks, a type foundry in Japan:

> Could I ask you a question about the MarkToBase in the GPOS table in the OpenType spec?
> It says:
>  
> "To combine the mark and base glyph, the client aligns their attachment points, positioning the mark with respect to the final pen point (advance) position of the base glyph."
>  
> The above is the first sentence where "attachment points" appear in the LookupType 4.
> I think the points are used for the same meaning as anchor points in the context. Am I correct?
> If so, why are these two points used separately here?
>  
> Moreover I have been having a hard time understanding the "positioning the mark with respect to the final pen point (advance) position of the base glyph" part.
> It says "the client aligns their attachment points" and that means the mark has been already positioned but why does it say ",positioning the mark ...base glyph" again?
>  
> Because I am a non-native English speaker, it may be over my head.
> The more I read it, the more it gets complicated.

In addition to getting some clarification that I can provide to this gentlemen, perhaps this is also an opportunity to make the specification clearer so that such questions do not need to asked. I have never used MarkToBase, so I am at a loss.

Regards...

-- Ken