/**
   * Process this instruction
   *
   * @param context the dynamic context of the transformation
   * @return a TailCall to be executed by the caller, always null for this instruction
   */
  public TailCall processLeavingTail(XPathContext context) throws XPathException {
    Controller controller = context.getController();
    SequenceReceiver out = context.getReceiver();
    int opt = options;
    int ann = annotation;

    // we may need to change the namespace prefix if the one we chose is
    // already in use with a different namespace URI: this is done behind the scenes
    // by the Outputter

    CharSequence value = expandChildren(context);
    if (schemaType != null) {
      // test whether the value actually conforms to the given type
      XPathException err =
          schemaType.validateContent(
              value,
              DummyNamespaceResolver.getInstance(),
              context.getConfiguration().getNameChecker());
      if (err != null) {
        ValidationException verr =
            new ValidationException(
                "Attribute value "
                    + Err.wrap(value, Err.VALUE)
                    + " does not the match the required type "
                    + schemaType.getDescription()
                    + ". "
                    + err.getMessage());
        verr.setErrorCode("XTTE1540");
        verr.setLocator(this);
        throw verr;
      }
    } else if (validationAction == Validation.STRICT || validationAction == Validation.LAX) {
      try {
        ann = controller.getConfiguration().validateAttribute(nameCode, value, validationAction);
      } catch (ValidationException e) {
        DynamicError err = DynamicError.makeDynamicError(e);
        String errorCode = e.getErrorCodeLocalPart();
        if (errorCode == null) {
          errorCode = (validationAction == Validation.STRICT ? "XTTE1510" : "XTTE1515");
        }
        err.setErrorCode(errorCode);
        err.setXPathContext(context);
        err.setLocator(this);
        err.setIsTypeError(true);
        throw err;
      }
    }
    try {
      out.attribute(nameCode, ann, value, locationId, opt);
    } catch (XPathException err) {
      throw dynamicError(this, err, context);
    }

    return null;
  }
  /** Evaluate in a general context */
  public Item evaluateItem(XPathContext c) throws XPathException {
    StringValue sv = (StringValue) argument[0].evaluateItem(c);
    if (sv == null) {
      return StringValue.EMPTY_STRING;
    }

    byte fb = Normalizer.C;
    if (argument.length == 2) {
      String form = argument[1].evaluateAsString(c).trim();
      if (form.equalsIgnoreCase("NFC")) {
        fb = Normalizer.C;
      } else if (form.equalsIgnoreCase("NFD")) {
        fb = Normalizer.D;
      } else if (form.equalsIgnoreCase("NFKC")) {
        fb = Normalizer.KC;
      } else if (form.equalsIgnoreCase("NFKD")) {
        fb = Normalizer.KD;
      } else if (form.equalsIgnoreCase("")) {
        return sv;
      } else {
        String msg = "Normalization form " + form + " is not supported";
        DynamicError err = new DynamicError(msg);
        err.setErrorCode("FOCH0003");
        err.setXPathContext(c);
        err.setLocator(this);
        throw err;
      }
    }

    // fast path for ASCII strings: normalization is a no-op
    boolean allASCII = true;
    CharSequence chars = sv.getStringValueCS();
    if (chars instanceof CompressedWhitespace) {
      return sv;
    }
    for (int i = chars.length() - 1; i >= 0; i--) {
      if (chars.charAt(i) > 127) {
        allASCII = false;
        break;
      }
    }
    if (allASCII) {
      return sv;
    }

    Normalizer norm = new Normalizer(fb);
    CharSequence result = norm.normalize(sv.getStringValueCS());
    return StringValue.makeStringValue(result);
  }
  public Item evaluateItem(XPathContext context) throws XPathException {
    Orphan o = (Orphan) super.evaluateItem(context);
    if (schemaType != null) {
      XPathException err =
          schemaType.validateContent(
              o.getStringValueCS(),
              DummyNamespaceResolver.getInstance(),
              context.getConfiguration().getNameChecker());
      if (err != null) {
        throw new ValidationException(
            "Attribute value "
                + Err.wrap(o.getStringValueCS(), Err.VALUE)
                + " does not the match the required type "
                + schemaType.getDescription()
                + ". "
                + err.getMessage());
      }
      o.setTypeAnnotation(schemaType.getFingerprint());
      if (schemaType.isNamespaceSensitive()) {
        throw new DynamicError(
            "Cannot validate a parentless attribute whose content is namespace-sensitive");
      }
    } else if (validationAction == Validation.STRICT || validationAction == Validation.LAX) {
      try {
        int ann =
            context
                .getController()
                .getConfiguration()
                .validateAttribute(nameCode, o.getStringValueCS(), validationAction);
        o.setTypeAnnotation(ann);
      } catch (ValidationException e) {
        DynamicError err = DynamicError.makeDynamicError(e);
        err.setErrorCode(e.getErrorCodeLocalPart());
        err.setXPathContext(context);
        err.setLocator(this);
        err.setIsTypeError(true);
        throw err;
      }
    }

    return o;
  }