code: public DescriptorMergeStrategy getStrategy(String descriptorUrl, Document descriptorDom) {
          for (Map.Entry<String, DescriptorMergeStrategy> entry : urlPatternToStrategyMappings.entrySet()) {
              if (descriptorUrl.matches(entry.getKey())) {
                  return entry.getValue();
              }
          }
  
          return null;
      }
docs: Returns a {@link DescriptorMergeStrategy} for a given descriptor, picked by matching the descriptor URL to a
  pattern associated to the strategy.
  
  @param descriptorUrl the URL that identifies the descriptor
  @param descriptorDom the XML DOM of the descriptor
  @return the {@link DescriptorMergeStrategy} for the descriptor, or null if the descriptor URL doesn't
  match any pattern.