It is my understanding that this means that in the header of the xml document there is a reference to a stylesheet and that reference is fully specified and available to the receiver (meaning that they are able to access that link and download that stylesheet)
In this example
<?xml-stylesheet type="text/xsl" href="CCD.XSL"?>
<ClinicalDocument xmlns="urn:hl7-org:v3" xmlns:xsi="
http://www.w3.org/2001/XMLSchema-instance" xmlns:cda="urn:hl7-org:v3">
<realmCode code="US" />
<typeId root="2.16.840.1.113883.1.3" extension="POCD_HD000040" />
The href only specifies CCD.XSL. If that were locally available to the receiver they could use that stylesheet.
That is my understanding and I hope that someone from PCC can speak to this to confirm and/or add information.