code: public static final boolean isSystemLiteral(String s) throws NullPointerException {
          try {
              checkSystemLiteral(s);
              return true;
          } catch (InvalidXMLException exception) {
              return false;
          }
      }
docs: Determines if the specified string matches the <em>SystemLiteral</em> production.
  See: <a href="http://www.w3.org/TR/REC-xml#NT-SystemLiteral">Definition of SystemLiteral</a>.
  
  @param s the character string to check, cannot be <code>null</code>.
  @return <code>true</code> if the {@link String} matches the production, or <code>false</code>
  otherwise.
  @throws NullPointerException if <code>s == null</code>.