code: public String getBaseIdentifier()
    {
  
      // Try to get the baseIdentifier from the baseIdentifier's stack,
      // which may not be the same thing as the value found in the
      // SourceLocators stack.
      String base = (String) (m_baseIdentifiers.isEmpty()
                              ? null : m_baseIdentifiers.peek());
  
      // Otherwise try the stylesheet.
      if (null == base)
      {
        SourceLocator locator = getLocator();
  
        base = (null == locator) ? "" : locator.getSystemId();
      }
  
      return base;
    }
docs: Return the base identifier.
  
  @return The base identifier of the current stylesheet.