Some more details on the written content improvement

[therahedwig]

So, doing the book research for the wiki, I ended up staring a lot at the contents via lua.

Here it is said everything above 0 is ignored.

df-structures/df.itemimprovements.xml

Line 186 in ff790ff

<stl-vector name='ref_aux' type-name='int32_t' comment='if nonzero, corresponding ref is ignored'/>

It seems that...
0 indicates that this is the main topic. Some books, like encyclopedias have multiple main topics. However, only the manual seems to teach anything. I suspect the learning about sites/people/regions/figures/events from books (and slabs, now I think about it), is not implemented at the moment.
1-4 I have not seen.
5 is for chronicles, biographies, autobiographies and cultural histories, the events here get written down as 'the first chapter concerns event x', so I suspect these are about chapters within a work.
6 is for poems, seems to in particular be about the values these espouse??? I can't find the description text of poems which have these refs.
7 is referencing poetry, this happens with musical compositions. Can be multiple.
8 is for choreographies, and references music compositions.
9 is for when academic works espouse a value.

I am still trying to figure out how value in written content exactly functions. I doubt only essays and dialogs (which have values as their main topic) adjust personal values. It's a bit tricky: histfigs mostly really like writing manuals and poems, and only manuals are bound to be written onto something.