Opening an existing drawing populated the style dialog but the selectors were not added to single style element. To achieve this, I played around with the map that contained selector names mapped to selector values (style attributes) of the object.
For every element that existed in the drawing already, I iterated the map of selectors. Appending each name and value to a string, the values of the resulting string were not in the order of insertion of selectors to this map. And then I learnt that maps contain key-value pairs in an ordered manner. The ordering occurs in a lexicographic manner irrespective of order of insertion of elements to it. Remember binary tree search? Well maps operate on the basis of this search algorithm.
So instead of using this map, I created a vector since order of insertion and retrieving elements has to be same.
std::map<std::string, std::string>_selectorMap; std::vector<std::pair<std::string, std::string> >_selectorVec;
Modification to move from map to vector was done at all places needed. Later I obtained nodes from XML representation of the document and added the content retrieved from the vector to a new child in the XML tree.