Changes made in JGRP-2764 seem to have made the JGroups XML Schema invalid.

For example, using a simple configuration file like:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:org:jgroups http://www.jgroups.org/schema/jgroups-5.3.xsd"
        xmlns="urn:org:jgroups">
 <BPING/>
</config>

When I try to validate it using xmllint:

$ xmllint --nowarning --noout --schema jgroups-5.3.xsd jgroups-test.xml 
jgroups-5.3.xsd:1500: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'type': References from this schema to components in the namespace 'fork' are not allowed, since not indicated by an import statement.
jgroups-5.3.xsd:7084: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'type': References from this schema to components in the namespace 'urn:jgroups:relay:1.0' are not allowed, since not indicated by an import statement.
jgroups-5.3.xsd:7188: element element: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'type': References from this schema to components in the namespace 'urn:jgroups:relay:1.0' are not allowed, since not indicated by an import statement.
WXS schema jgroups-5.3.xsd failed to compile

If I slightly modify jgroups-5.3.xsd like this:

$ diff -u jgroups-5.3.xsd jgroups-5.3-modified.xsd
--- jgroups-5.3.xsd    2024-03-01 09:25:22.000000000 +0100
+++ jgroups-5.3-modified.xsd    2024-08-19 10:41:30.391664175 +0200
@@ -1497,7 +1497,7 @@
       <xs:element name="FORK">
         <xs:complexType>
           <xs:choice maxOccurs="unbounded" minOccurs="0">
-            <xs:element name="fork-stacks" type="fork:ForkStacksType"/>
+            <xs:element name="fork-stacks" type="tns:ForkStacksType"/>
           </xs:choice>
           <xs:attribute name="after_creation_hook" type="xs:string">
             <xs:annotation>
@@ -7081,7 +7081,7 @@
       <xs:element name="relay.RELAY2">
         <xs:complexType>
           <xs:choice maxOccurs="unbounded" minOccurs="0">
-            <xs:element name="RelayConfiguration" type="relay:RelayConfigurationType"/>
+            <xs:element name="RelayConfiguration" type="tns:RelayConfigurationType"/>
           </xs:choice>
           <xs:attribute name="after_creation_hook" type="xs:string">
             <xs:annotation>
@@ -7185,7 +7185,7 @@
       <xs:element name="relay.RELAY3">
         <xs:complexType>
           <xs:choice maxOccurs="unbounded" minOccurs="0">
-            <xs:element name="RelayConfiguration" type="relay:RelayConfigurationType"/>
+            <xs:element name="RelayConfiguration" type="tns:RelayConfigurationType"/>
           </xs:choice>
           <xs:attribute name="after_creation_hook" type="xs:string">
             <xs:annotation>

I can then validate the file successfully:

$ xmllint --nowarning --noout --schema jgroups-5.3-modified.xsd jgroups-test.xml
jgroups-test.xml validates

Tools other than xmllint show the same issue by the way:

$ python3
>>> with open('jgroups-5.3.xsd', 'rb') as f:
...     root=etree.XML(f.read())
...     s=etree.XMLSchema(root)
... ^D
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "src/lxml/xmlschema.pxi", line 90, in lxml.etree.XMLSchema._init_
lxml.etree.XMLSchemaParseError: Element '{http://www.w3.org/2001/XMLSchema}element', attribute 'type': References from this schema to components in the namespace 'fork' are not allowed, since not indicated by an import statement., line 1500