The cpl_minixml.cpp is unable to consume the attached document with a complex DOCTYPE declaration that looks like this:
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE WMT_MS_Capabilities SYSTEM
"http://schemas.cubewerx.com/schemas/wms/1.1.2/WMT_MS_Capabilities.dtd"
[
<!-- vendor-specific elements defined here -->
<!ELEMENT VendorSpecificCapabilities (CubeSERV?)>
<!ELEMENT CubeSERV (Extract?, MultibandLayers?)>
<!ATTLIST CubeSERV version CDATA #REQUIRED>
<!ELEMENT Extract (ExtractableLayers, ArchiveFormats, DCPType+)>
<!ELEMENT ExtractableLayers (ExtractableLayer*)>
<!ELEMENT ExtractableLayer (ExtractFormat+)>
<!ATTLIST ExtractableLayer name CDATA #REQUIRED>
<!ELEMENT ExtractFormat EMPTY>
<!ATTLIST ExtractFormat name CDATA #REQUIRED>
<!ELEMENT ArchiveFormats (ArchiveFormat+)>
<!ELEMENT ArchiveFormat EMPTY>
<!ATTLIST ArchiveFormat name CDATA #REQUIRED>
<!ELEMENT MultibandLayers (MultibandLayer*)>
<!ELEMENT MultibandLayer EMPTY>
<!ATTLIST MultibandLayer name CDATA #REQUIRED numOfChannels CDATA #REQUIRED>
]>
...