Description
The "Standalone Document Declaration" [1] validity constraint applies to markup declarations which occur in the external subset and/or a parameter entity (also known as external markup declarations [2]). Xerces is only considering declarations in the external subset when it checks this constraint.
[1] http://www.w3.org/TR/2006/REC-xml-20060816/#vc-check-rmd
[2] http://www.w3.org/TR/2006/REC-xml-20060816/#dt-extmkpdecl