In the first category, a link which might be an HTML or other URL
link will not be shown as unresolved, and nor will be a link that
starts with ‘/’ (a reference to the content of a different topic,
or a command).
Files of size 0 are not checked in either category (they are not
considered to be part of the topic).
As a special case, the content of the file tag of a reference
is treated as a link to a file in the files collection, and therefore