diff --git a/README.md b/README.md
index 34ea71e..ecc7376 100644
--- a/README.md
+++ b/README.md
@@ -8,3 +8,39 @@ Place [relative-xopp-background](relative-xopp-background) in `~/.local/share/na
If missing, install [notify2](https://pypi.org/project/notify2/) and (optionally)
[dbus-python](https://pypi.org/project/dbus-python/) with your package manager or with pip.
+
+## Details
+
+Here is an excerpt of a Xournal++ document `/home/user/notes/note1/paper.pdf.xopp`:
+
+```xml
+
+
+ Xournal++ document - see https://github.com/xournalpp/xournalpp
+
+
+
+
+
+
+
+```
+
+If the background PDF file `/home/user/Documents/paper.pdf` does not exist
+but `/home/user/notes/note1/paper.pdf` is accessible (which is in the same folder as the Xournal++ file),
+then the absolute path will be replaced with a path relative one:
+
+```xml
+
+
+ Xournal++ document - see https://github.com/xournalpp/xournalpp
+
+
+
+
+
+
+
+```