private void verifyUsedAttributes(PreprocessorReader reader, Map<String, Object> attributes) {
          String unsupportedAttributes = attributes
            .keySet()
            .stream()
            .filter(attribute ->
              "leveloffset".equals(attribute) || "encoding".equals(attribute) || "opts".equals(attribute))
            .collect(joining(", "));

          if (!unsupportedAttributes.isEmpty()) {
            throw new RuntimeException(format("%s: line %d: unsupported attributes in custom include directive, " +
                "if you need them, their logic first has to be replicated in %s: %s",
              reader.getFile(), reader.getLineNumber() - 1, getClass().getSimpleName(), unsupportedAttributes));
          }
        }
As we do custom include handling here, we have to reimplement all attribute handling we need.
So verify that only currently supported attributes are used.

@param reader The current reader
@param attributes The attributes used on the include directive
build-logic/asciidoc-extensions/src/main/java/org/spockframework/plugins/asciidoctor/IncludedSourceLinker.java