public abstract class Escaper {
  // TODO(dbeaumont): evaluate custom implementations, considering package private constructor.
  /** Constructor for use by subclasses. */
  protected Escaper() {}

  /**
   * Returns the escaped form of a given literal string.
   *
   * <p>Note that this method may treat input characters differently depending on the specific
   * escaper implementation.
   *
   * <ul>

   *
   */
  public static Escaper urlFormParameterEscaper() {
    return URL_FORM_PARAMETER_ESCAPER;
  }

  private static final Escaper URL_FORM_PARAMETER_ESCAPER =
      new PercentEscaper(URL_FORM_PARAMETER_OTHER_SAFE_CHARS, true);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in <a

   *
   */
  public static Escaper urlFormParameterEscaper() {
    return URL_FORM_PARAMETER_ESCAPER;
  }

  private static final Escaper URL_FORM_PARAMETER_ESCAPER =
      new PercentEscaper(URL_FORM_PARAMETER_OTHER_SAFE_CHARS, true);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in <a

<%@page pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"%>
<meta content='width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no' name='viewport'>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<link href="${fe:url('/css/admin/bootstrap.min.css')}" rel="stylesheet" type="text/css" />
<link href="${fe:url('/css/admin/font-awesome.min.css')}" rel="stylesheet" type="text/css" />

  /**
   * Asserts that an escaper behaves correctly with respect to null inputs.
   *
   * @param escaper the non-null escaper to test
   */
  public static void assertBasic(Escaper escaper) throws IOException {
    // Escapers operate on characters: no characters, no escaping.
    Assert.assertEquals("", escaper.escape(""));
    // Assert that escapers throw null pointer exceptions.
    try {
      escaper.escape((String) null);

  /**
   * Asserts that an escaper behaves correctly with respect to null inputs.
   *
   * @param escaper the non-null escaper to test
   */
  public static void assertBasic(Escaper escaper) throws IOException {
    // Escapers operate on characters: no characters, no escaping.
    Assert.assertEquals("", escaper.escape(""));
    // Assert that escapers throw null pointer exceptions.
    try {
      escaper.escape((String) null);

/**
 * Static utility methods pertaining to {@link Escaper} instances.
 *
 * @author Sven Mawson
 * @author David Beaumont
 * @since 15.0
 */
@GwtCompatible
public final class Escapers {
  private Escapers() {}

  /**
   * Returns an {@link Escaper} that does no escaping, passing all character data through unchanged.
   */
  public static Escaper nullEscaper() {
    return NULL_ESCAPER;
  }

   * output.
   *
   * <p>This escaper does not treat surrogate pairs specially and does not perform Unicode
   * validation on its input.
   */
  @SuppressWarnings("EscapedEntity") // We do mean for the user to see &#x9;" etc.
  public static Escaper xmlAttributeEscaper() {
    return XML_ATTRIBUTE_ESCAPER;
  }

  private static final Escaper XML_ESCAPER;
  private static final Escaper XML_CONTENT_ESCAPER;

    Escaper escaper = Escapers.builder().setSafeRange('a', 'z').build();
    assertThat(escaper.escape("The Quick Brown Fox")).isEqualTo("The Quick Brown Fox");
  }

  public void testBuilderInitialStateNoneUnsafe() {
    // No characters are unsafe by default (safeMin == 0, safeMax == 0xFFFF).
    Escaper escaper = Escapers.builder().setUnsafeReplacement("X").build();

            k <= bias -> TMIN
            k >= bias + TMAX -> TMAX
            else -> k - bias
          }
        if (digit < t) break
        val scaleW = BASE - t
        if (w > Int.MAX_VALUE / scaleW) return false // Prevent overflow.
        w *= scaleW
      }
      bias = adapt(i - oldi, codePoints.size + 1, oldi == 0)
      val deltaN = i / (codePoints.size + 1)