docs: public String getFullContentType() {
          final String url = this.url.toExternalForm().substring("data:".length());
          final int endIndex = url.indexOf(',');
          if (endIndex >= 0) {
              final String contentType = url.substring(0, endIndex);
              if (!contentType.isEmpty()) {
                  return contentType;
              }
          }
          return "text/plain;charset=US-ASCII";
      }