code: public int getVariableId(String attrId) throws MIDDParsingException {
          if (!attributeMapper.containsKey(attrId)) {
              throw new MIDDParsingException("Attribute '" + attrId + "' not found");
          }
  
          return attributeMapper.get(attrId).intValue();
      }
docs: /*
  Return the variable identifier from the attribute-id