[Orgmode] user-defined agenda sorting

[Samuel Wales]

I have a sort comparison function for the outline, which
returns a number.  This works well.

The documentation for user-defined agenda sorting says "This
function must receive two arguments, agenda entry a and b."
I am not sure what a and b are, strings?

My function gets priorities, tags, and todo kw assuming point is on a
headline.  It uses org functions to get those.  The org code for
agenda sorting uses text properties.

How to adapt my function to get the following information: priorities
as [?A..?C], inherited and local tags as a list, and todo kw as a
string?

Is there a place where how to parse a and b is documented?

Thanks.

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