Create a space with a name like, say, '& this is how the tree breaks' and try to export a page within the space as a PDF. You'll find this:

Caused by: org.apache.fop.apps.FOPException: The entity name must immediately follow the '&' in the entity reference.
at org.apache.fop.apps.Driver.render(Driver.java:503)
at org.apache.fop.apps.Driver.run(Driver.java:565)
at com.atlassian.confluence.importexport.impl.PdfExporter.generatePDF(PdfExporter.java:158)
... 78 more