When content is to be exported as XML or XHTML the document must first be marked accordingly. For this purpose, a corresponding XML marker such as
<?xml version="1.0"?>
at the beginning of a line or XHTML marker such as
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
must be exported first. Both tags must be placed at the
beginning of the exported document. They are not recognized
when they are contained in processing instructions
(<? ... >) or are part of an
SGML comment
(<!-- ... -->).
The markers not only serve the client (mostly the browser) to determine the type of the document but also influence the export of so called empty element tags. These tags are exported as such when at least one of the following two conditions is met:
The empty element tag is contained in the content part (in a field) to be exported.
The empty element tag is generated by an NPSOBJ
instruction (e.g. <npsobj insertvalue="image"
name="..." /> and an XML or XHTML marker was
exported before.
In all other cases no empty element tags but single tags without closing slash are exported.