code: private static Pattern importStringToPattern(boolean allowModules, String s, Processor p, Log log) {
          String module;
          String pkg;
          int slash = s.indexOf('/');
          if (slash == (-1)) {
              if (s.equals("*")) {
                  return MatchingUtils.validImportStringToPattern(s);
              }
              module = allowModules ? ".*/" : "";
              pkg = s;
          } else {
              module = Pattern.quote(s.substring(0, slash + 1));
              pkg = s.substring(slash + 1);
          }
          if (MatchingUtils.isValidImportString(pkg)) {
              return Pattern.compile(module + MatchingUtils.validImportStringToPatternString(pkg));
          } else {
              log.warning("proc.malformed.supported.string", s, p.getClass().getName());
              return noMatches; // won't match any valid identifier
          }
      }
docs: Convert import-style string for supported annotations into a
  regex matching that string.  If the string is not a valid
  import-style string, return a regex that won't match anything.