Example: Missing Entity

External parsed entities may disappear from XML documents

<?xml version="1.0" standalone="no"?>
<!DOCTYPE doc [
<!ENTITY contents SYSTEM "separatefile.xml">
]>
<doc>
&contents;
</doc>

A non-validating parser may report:
```
<doc/>
```
Just a warning... Non-validating parsers are supposed to report the missing entity retrieval to the application, so that it has a chance to collect the information, but this requires code that doesn't always get written...