exiv2 does not register certain namespaces present in an image

Describe the bug

Certain xmp namespaces that we know are present in an image, do not get registered. When trying to retrieve the namespace it throws "No namespace info available for XMP prefix `Item'".

This is known to happen with:

prefix Item - namespace http://ns.google.com/photos/1.0/container/item/ (see GIMP issue https://gitlab.gnome.org/GNOME/gimp/-/issues/10557.
prefix apple-fi

To Reproduce

Steps to reproduce the behavior:

Use the image from the above linked GIMP issue: https://shallowsky.com/tmp/PXL_20231220_182442817.jpg Note only the direct link works since Gitlab removes most metadata.
Build and run the supplied sample program on the above image. (attaching a zip doesn't seem to work, so replaced cpp with txt) test-namespace.txt

Tested on Windows 10 Home, 64-bit using: MINGW64:

$ ./namespace-test.sh
+++ Testing exiv2 namespace info (exiv2 version 0.27.7)
Container namespace: 'http://ns.google.com/photos/1.0/container/'.
Exiv2 exception: 'No namespace info available for XMP prefix `Item''

UCRT64:

$ ./namespace-test.sh
Testing exiv2 namespace info (exiv2 version 0.28.2)
Container namespace: 'http://ns.google.com/photos/1.0/container/'.
Exiv2 exception: 'No namespace info available for XMP prefix `Item''

Expected behavior

I expect it to return the namespace for the Item prefix just like it does for Container.

Desktop (please complete the following information):

OS and version: Windows 10 Home, 64-bit
Exiv2 version and source: MINGW64 0.27.7, UCRT64 0.28.2
Compiler and version: default as chosen by the MSYS2 project
Compilation mode and/or compiler flags: as above

Additional context

Same on Linux using 0.28.2:

$ ./a.out PXL_20231220_182442817.jpg
Testing exiv2 namespace info (exiv2 version 0.28.2)
Container namespace: 'http://ns.google.com/photos/1.0/container/'.
Exiv2 exception: 'No namespace info available for XMP prefix `Item'

Still trying to understand the issue though.

It do seam to dump the namespace/container info properly (?):

$ exiv2 -PX ./PXL_20231220_182442817.jpg
Xmp.hdrgm.Version                            XmpText     3  1.0
Xmp.xmpNote.HasExtendedXMP                   XmpText    32  9AABF2DA602006640FE14B0C857436F3
Xmp.Container.Directory                      XmpText     0  type="Seq"
Xmp.Container.Directory[1]                   XmpText     0  type="Struct"
Xmp.Container.Directory[1]/Container:Item    XmpText     0  type="Struct"
Xmp.Container.Directory[1]/Container:Item/Item:Mime XmpText    10  image/jpeg
Xmp.Container.Directory[1]/Container:Item/Item:Semantic XmpText     7  Primary
Xmp.Container.Directory[2]                   XmpText     0  type="Struct"
Xmp.Container.Directory[2]/Container:Item    XmpText     0  type="Struct"
Xmp.Container.Directory[2]/Container:Item/Item:Mime XmpText    10  image/jpeg
Xmp.Container.Directory[2]/Container:Item/Item:Semantic XmpText     7  GainMap
Xmp.Container.Directory[2]/Container:Item/Item:Length XmpText     6  207318

Result of image->xmpPacket() do seam to contain stuff as well:

<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?> 
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 4.4.0-Exiv2">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
   <rdf:Description rdf:about="" xmlns:hdrgm="http://ns.adobe.com/hdr-gain-map/1.0/" xmlns:xmpNote="http://ns.adobe.com/xmp/note/" xmlns:Container="http://ns.google.com/photos/1.0/container/" xmlns:Item="http://ns.google.com/photos/1.0/container/item/" hdrgm:Version="1.0" xmpNote:HasExtendedXMP="9AABF2DA602006640FE14B0C857436F3">
   <Container:Directory>
      <rdf:Seq>
         <rdf:li rdf:parseType="Resource">
           <Container:Item Item:Mime="image/jpeg" Item:Semantic="Primary"/>
         </rdf:li>
         <rdf:li rdf:parseType="Resource">
            <Container:Item Item:Mime="image/jpeg" Item:Semantic="GainMap" Item:Length="207318"/>
         </rdf:li>
        </rdf:Seq>
      </Container:Directory>
    </rdf:Description>
  </rdf:RDF>
</x:xmpmeta>

Also, the list of registered namespaces only contains "Container namespace" (and bunch of other, unrelated ones):

    Exiv2::Dictionary ns_dict;
    Exiv2::XmpProperties::registeredNamespaces(ns_dict);
    for (auto const& entry : ns_dict)
    {
        std::cout << entry.first << ": " << entry.second << std::endl;
    }

...
...
xmpRights: http://ns.adobe.com/xap/1.0/rights/
xmpT: http://ns.adobe.com/xap/1.0/t/
xmpTPg: http://ns.adobe.com/xap/1.0/t/pg/
xmpidq: http://ns.adobe.com/xmp/Identifier/qual/1.0/
Container namespace: 'http://ns.google.com/photos/1.0/container/'.

It would seem, that http://ns.adobe.com/hdr-gain-map/1.0/" is also missing o_0

But despite everything, accessing by explicit key works:

$ exiv2 -K "Xmp.Container.Directory[1]/Container:Item" ./PXL_20231220_182442817.jpg
Xmp.Container.Directory[1]/Container:Item    XmpText     0  type="Struct"

o_0

Exiv2 / exiv2