@CanIgnoreReturnValue
  public CharEscaperBuilder addEscape(char c, String r) {
    map.put(c, checkNotNull(r));
    if (c > max) {
      max = c;
    }
    return this;
  }

  /** Add multiple mappings at once for a particular index. */
  @CanIgnoreReturnValue
  public CharEscaperBuilder addEscapes(char[] cs, String r) {
    checkNotNull(r);
    for (char c : cs) {
      addEscape(c, r);
    }
    return this;
  }

    builder.setUnsafeReplacement("X");
    builder.addEscape(' ', "_");
    Escaper first = builder.build();
    // Modify one of the existing mappings before creating a new escaper.
    builder.addEscape(' ', "-");
    builder.addEscape('!', "$");
    Escaper second = builder.build();
    // This should have no effect on existing escapers.
    builder.addEscape(' ', "*");

    // Test both escapers after modifying the builder.

        builder.addEscape(c, "\uFFFD");
      }
    }

    // Build the content escaper first and then add quote escaping for the
    // general escaper.
    builder.addEscape('&', "&");
    builder.addEscape('<', "&lt;");
    builder.addEscape('>', "&gt;");
    XML_CONTENT_ESCAPER = builder.build();
    builder.addEscape('\'', "&apos;");
    builder.addEscape('"', "&quot;");