Comprehension question about docbook5 and xmllint

Hi,

I try to create one big xml file from my modularized documents with xmllint.

_My files can be found here:_
https://github.com/mepi0011/darktable/tree/docBook5_port/doc/usermanual

_The Command I use is:_

xmllint --xinclude --output big.xml darktable.xml

But I run into some errors:

darktable.xml:32: parser error : Entity 'eacute' not defined 

If I comment out the corresponding lines in the document darktable.xml, the command 
runs without further errors. Although entities are used in the documents inserted with 
Xinclude. The subdocuments always link to the same docbook.ent file in the same 
folder as darktable.xml.


If I apply the command individually to subdocuments, I also receive the corresponding 
error messages.

Why do I get the error messages?
Is this caused by my declaration of entities or xmllint?

Thanks
Pierre