private @Nullable PsiElement getValueElement(PsiFile baseFile) {
    final XmlAttributeValue attributeValue = getValueElement();
    if (isInternalReference()) return attributeValue;

    if (attributeValue != null) {
      final String value = attributeValue.getValue();
      XmlFile xmlFile = XmlUtil.findNamespaceByLocation(baseFile, value);
      if (xmlFile != null) {
        return xmlFile;
      }

      final int i = XmlUtil.getPrefixLength(value);
      if (i > 0) {
        return XmlUtil.findNamespaceByLocation(baseFile, value.substring(i));
      }
    }

    return null;
  }
private @Nullable PsiElement getValueElement(PsiFile baseFile)