code: @Nonnull
    @Nonempty
    public static String getEscapedCSSURL (@Nonnull final String sURL, final char cQuoteChar)
    {
      ValueEnforcer.notNull (sURL, "URL");
  
      if (sURL.indexOf (cQuoteChar) < 0 && sURL.indexOf (CSSParseHelper.URL_ESCAPE_CHAR) < 0)
      {
        // Found nothing to quote
        return sURL;
      }
  
      final StringBuilder aSB = new StringBuilder (sURL.length () * 2);
      for (final char c : sURL.toCharArray ())
      {
        // Escape the quote char and the escape char itself
        if (c == cQuoteChar || c == CSSParseHelper.URL_ESCAPE_CHAR)
          aSB.append (CSSParseHelper.URL_ESCAPE_CHAR);
        aSB.append (c);
      }
      return aSB.toString ();
    }
docs: Internal method to escape a CSS URL. Because this method is only called for
  quoted URLs, only the quote character itself needs to be quoted.
  
  @param sURL
  The URL to be escaped. May not be <code>null</code>.
  @param cQuoteChar
  The quote char that is used. Either '\'' or '"'
  @return The escaped string. Never <code>null</code>.