Your metadata has this structure (hmm... perhaps some of the Inlines are really MetaInlines, in which case that's a problem with my logging module):
(#) meta Meta {
author: List[2] {
[1] Inlines[3] {
[1] Str "Author"
[2] Space
[3] Str "A"
}
[2] Inlines[3] {
[1] Str "Author"
[2] Space
[3] Str "B"
}
}
title: Inlines[1] {
[1] Str "Test"
}
}
... so I think you want this filter (MetaInlines isn't an attribute name, and you have to count the space):
function Meta (m)
print(pandoc.utils.stringify(m.author[1][3]))
end