docs: public static <T extends ContentMeta> ResourceSelector<T> regexMetadataResourceSelector(final Map<String,
              String> required, final boolean requireAll) {
          return new ResourceSelector<T>() {
              Map<String, Pattern> patternMap = new HashMap<String, Pattern>();
  
              private Pattern forString(String regex) {
                  if (null == patternMap.get(regex)) {
                      Pattern compile = null;
                      try {
                          compile = Pattern.compile(regex);
                      } catch (PatternSyntaxException ignored) {
                          return null;
                      }
                      patternMap.put(regex, compile);
                  }
                  return patternMap.get(regex);
              }
  
              @Override
              public boolean matchesContent(T content) {
                  for (String key : required.keySet()) {
                      Pattern pattern = forString(required.get(key));
                      String test = content.getMeta().get(key);
                      if (null != test && null != pattern && pattern.matcher(test).matches()) {
                          if (!requireAll) {
                              return true;
                          }
                      } else if (requireAll) {
                          return false;
                      }
                  }
                  return requireAll;
              }
          };
      }