Source file src/encoding/xml/xml.go

Documentation: encoding/xml

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package xml implements a simple XML 1.0 parser that
     6  // understands XML name spaces.
     7  package xml
     8  
     9  // References:
    10  //    Annotated XML spec: https://www.xml.com/axml/testaxml.htm
    11  //    XML name spaces: https://www.w3.org/TR/REC-xml-names/
    12  
    13  // TODO(rsc):
    14  //	Test error handling.
    15  
    16  import (
    17  	"bufio"
    18  	"bytes"
    19  	"errors"
    20  	"fmt"
    21  	"io"
    22  	"strconv"
    23  	"strings"
    24  	"unicode"
    25  	"unicode/utf8"
    26  )
    27  
    28  // A SyntaxError represents a syntax error in the XML input stream.
    29  type SyntaxError struct {
    30  	Msg  string
    31  	Line int
    32  }
    33  
    34  func (e *SyntaxError) Error() string {
    35  	return "XML syntax error on line " + strconv.Itoa(e.Line) + ": " + e.Msg
    36  }
    37  
    38  // A Name represents an XML name (Local) annotated
    39  // with a name space identifier (Space).
    40  // In tokens returned by Decoder.Token, the Space identifier
    41  // is given as a canonical URL, not the short prefix used
    42  // in the document being parsed.
    43  type Name struct {
    44  	Space, Local string
    45  }
    46  
    47  // An Attr represents an attribute in an XML element (Name=Value).
    48  type Attr struct {
    49  	Name  Name
    50  	Value string
    51  }
    52  
    53  // A Token is an interface holding one of the token types:
    54  // StartElement, EndElement, CharData, Comment, ProcInst, or Directive.
    55  type Token interface{}
    56  
    57  // A StartElement represents an XML start element.
    58  type StartElement struct {
    59  	Name Name
    60  	Attr []Attr
    61  }
    62  
    63  // Copy creates a new copy of StartElement.
    64  func (e StartElement) Copy() StartElement {
    65  	attrs := make([]Attr, len(e.Attr))
    66  	copy(attrs, e.Attr)
    67  	e.Attr = attrs
    68  	return e
    69  }
    70  
    71  // End returns the corresponding XML end element.
    72  func (e StartElement) End() EndElement {
    73  	return EndElement{e.Name}
    74  }
    75  
    76  // An EndElement represents an XML end element.
    77  type EndElement struct {
    78  	Name Name
    79  }
    80  
    81  // A CharData represents XML character data (raw text),
    82  // in which XML escape sequences have been replaced by
    83  // the characters they represent.
    84  type CharData []byte
    85  
    86  func makeCopy(b []byte) []byte {
    87  	b1 := make([]byte, len(b))
    88  	copy(b1, b)
    89  	return b1
    90  }
    91  
    92  // Copy creates a new copy of CharData.
    93  func (c CharData) Copy() CharData { return CharData(makeCopy(c)) }
    94  
    95  // A Comment represents an XML comment of the form <!--comment-->.
    96  // The bytes do not include the <!-- and --> comment markers.
    97  type Comment []byte
    98  
    99  // Copy creates a new copy of Comment.
   100  func (c Comment) Copy() Comment { return Comment(makeCopy(c)) }
   101  
   102  // A ProcInst represents an XML processing instruction of the form <?target inst?>
   103  type ProcInst struct {
   104  	Target string
   105  	Inst   []byte
   106  }
   107  
   108  // Copy creates a new copy of ProcInst.
   109  func (p ProcInst) Copy() ProcInst {
   110  	p.Inst = makeCopy(p.Inst)
   111  	return p
   112  }
   113  
   114  // A Directive represents an XML directive of the form <!text>.
   115  // The bytes do not include the <! and > markers.
   116  type Directive []byte
   117  
   118  // Copy creates a new copy of Directive.
   119  func (d Directive) Copy() Directive { return Directive(makeCopy(d)) }
   120  
   121  // CopyToken returns a copy of a Token.
   122  func CopyToken(t Token) Token {
   123  	switch v := t.(type) {
   124  	case CharData:
   125  		return v.Copy()
   126  	case Comment:
   127  		return v.Copy()
   128  	case Directive:
   129  		return v.Copy()
   130  	case ProcInst:
   131  		return v.Copy()
   132  	case StartElement:
   133  		return v.Copy()
   134  	}
   135  	return t
   136  }
   137  
   138  // A TokenReader is anything that can decode a stream of XML tokens, including a
   139  // Decoder.
   140  //
   141  // When Token encounters an error or end-of-file condition after successfully
   142  // reading a token, it returns the token. It may return the (non-nil) error from
   143  // the same call or return the error (and a nil token) from a subsequent call.
   144  // An instance of this general case is that a TokenReader returning a non-nil
   145  // token at the end of the token stream may return either io.EOF or a nil error.
   146  // The next Read should return nil, io.EOF.
   147  //
   148  // Implementations of Token are discouraged from returning a nil token with a
   149  // nil error. Callers should treat a return of nil, nil as indicating that
   150  // nothing happened; in particular it does not indicate EOF.
   151  type TokenReader interface {
   152  	Token() (Token, error)
   153  }
   154  
   155  // A Decoder represents an XML parser reading a particular input stream.
   156  // The parser assumes that its input is encoded in UTF-8.
   157  type Decoder struct {
   158  	// Strict defaults to true, enforcing the requirements
   159  	// of the XML specification.
   160  	// If set to false, the parser allows input containing common
   161  	// mistakes:
   162  	//	* If an element is missing an end tag, the parser invents
   163  	//	  end tags as necessary to keep the return values from Token
   164  	//	  properly balanced.
   165  	//	* In attribute values and character data, unknown or malformed
   166  	//	  character entities (sequences beginning with &) are left alone.
   167  	//
   168  	// Setting:
   169  	//
   170  	//	d.Strict = false
   171  	//	d.AutoClose = xml.HTMLAutoClose
   172  	//	d.Entity = xml.HTMLEntity
   173  	//
   174  	// creates a parser that can handle typical HTML.
   175  	//
   176  	// Strict mode does not enforce the requirements of the XML name spaces TR.
   177  	// In particular it does not reject name space tags using undefined prefixes.
   178  	// Such tags are recorded with the unknown prefix as the name space URL.
   179  	Strict bool
   180  
   181  	// When Strict == false, AutoClose indicates a set of elements to
   182  	// consider closed immediately after they are opened, regardless
   183  	// of whether an end element is present.
   184  	AutoClose []string
   185  
   186  	// Entity can be used to map non-standard entity names to string replacements.
   187  	// The parser behaves as if these standard mappings are present in the map,
   188  	// regardless of the actual map content:
   189  	//
   190  	//	"lt": "<",
   191  	//	"gt": ">",
   192  	//	"amp": "&",
   193  	//	"apos": "'",
   194  	//	"quot": `"`,
   195  	Entity map[string]string
   196  
   197  	// CharsetReader, if non-nil, defines a function to generate
   198  	// charset-conversion readers, converting from the provided
   199  	// non-UTF-8 charset into UTF-8. If CharsetReader is nil or
   200  	// returns an error, parsing stops with an error. One of the
   201  	// CharsetReader's result values must be non-nil.
   202  	CharsetReader func(charset string, input io.Reader) (io.Reader, error)
   203  
   204  	// DefaultSpace sets the default name space used for unadorned tags,
   205  	// as if the entire XML stream were wrapped in an element containing
   206  	// the attribute xmlns="DefaultSpace".
   207  	DefaultSpace string
   208  
   209  	r              io.ByteReader
   210  	t              TokenReader
   211  	buf            bytes.Buffer
   212  	saved          *bytes.Buffer
   213  	stk            *stack
   214  	free           *stack
   215  	needClose      bool
   216  	toClose        Name
   217  	nextToken      Token
   218  	nextByte       int
   219  	ns             map[string]string
   220  	err            error
   221  	line           int
   222  	offset         int64
   223  	unmarshalDepth int
   224  }
   225  
   226  // NewDecoder creates a new XML parser reading from r.
   227  // If r does not implement io.ByteReader, NewDecoder will
   228  // do its own buffering.
   229  func NewDecoder(r io.Reader) *Decoder {
   230  	d := &Decoder{
   231  		ns:       make(map[string]string),
   232  		nextByte: -1,
   233  		line:     1,
   234  		Strict:   true,
   235  	}
   236  	d.switchToReader(r)
   237  	return d
   238  }
   239  
   240  // NewTokenDecoder creates a new XML parser using an underlying token stream.
   241  func NewTokenDecoder(t TokenReader) *Decoder {
   242  	// Is it already a Decoder?
   243  	if d, ok := t.(*Decoder); ok {
   244  		return d
   245  	}
   246  	d := &Decoder{
   247  		ns:       make(map[string]string),
   248  		t:        t,
   249  		nextByte: -1,
   250  		line:     1,
   251  		Strict:   true,
   252  	}
   253  	return d
   254  }
   255  
   256  // Token returns the next XML token in the input stream.
   257  // At the end of the input stream, Token returns nil, io.EOF.
   258  //
   259  // Slices of bytes in the returned token data refer to the
   260  // parser's internal buffer and remain valid only until the next
   261  // call to Token. To acquire a copy of the bytes, call CopyToken
   262  // or the token's Copy method.
   263  //
   264  // Token expands self-closing elements such as <br/>
   265  // into separate start and end elements returned by successive calls.
   266  //
   267  // Token guarantees that the StartElement and EndElement
   268  // tokens it returns are properly nested and matched:
   269  // if Token encounters an unexpected end element
   270  // or EOF before all expected end elements,
   271  // it will return an error.
   272  //
   273  // Token implements XML name spaces as described by
   274  // https://www.w3.org/TR/REC-xml-names/. Each of the
   275  // Name structures contained in the Token has the Space
   276  // set to the URL identifying its name space when known.
   277  // If Token encounters an unrecognized name space prefix,
   278  // it uses the prefix as the Space rather than report an error.
   279  func (d *Decoder) Token() (Token, error) {
   280  	var t Token
   281  	var err error
   282  	if d.stk != nil && d.stk.kind == stkEOF {
   283  		return nil, io.EOF
   284  	}
   285  	if d.nextToken != nil {
   286  		t = d.nextToken
   287  		d.nextToken = nil
   288  	} else {
   289  		if t, err = d.rawToken(); t == nil && err != nil {
   290  			if err == io.EOF && d.stk != nil && d.stk.kind != stkEOF {
   291  				err = d.syntaxError("unexpected EOF")
   292  			}
   293  			return nil, err
   294  		}
   295  		// We still have a token to process, so clear any
   296  		// errors (e.g. EOF) and proceed.
   297  		err = nil
   298  	}
   299  	if !d.Strict {
   300  		if t1, ok := d.autoClose(t); ok {
   301  			d.nextToken = t
   302  			t = t1
   303  		}
   304  	}
   305  	switch t1 := t.(type) {
   306  	case StartElement:
   307  		// In XML name spaces, the translations listed in the
   308  		// attributes apply to the element name and
   309  		// to the other attribute names, so process
   310  		// the translations first.
   311  		for _, a := range t1.Attr {
   312  			if a.Name.Space == xmlnsPrefix {
   313  				v, ok := d.ns[a.Name.Local]
   314  				d.pushNs(a.Name.Local, v, ok)
   315  				d.ns[a.Name.Local] = a.Value
   316  			}
   317  			if a.Name.Space == "" && a.Name.Local == xmlnsPrefix {
   318  				// Default space for untagged names
   319  				v, ok := d.ns[""]
   320  				d.pushNs("", v, ok)
   321  				d.ns[""] = a.Value
   322  			}
   323  		}
   324  
   325  		d.translate(&t1.Name, true)
   326  		for i := range t1.Attr {
   327  			d.translate(&t1.Attr[i].Name, false)
   328  		}
   329  		d.pushElement(t1.Name)
   330  		t = t1
   331  
   332  	case EndElement:
   333  		d.translate(&t1.Name, true)
   334  		if !d.popElement(&t1) {
   335  			return nil, d.err
   336  		}
   337  		t = t1
   338  	}
   339  	return t, err
   340  }
   341  
   342  const (
   343  	xmlURL      = "http://www.w3.org/XML/1998/namespace"
   344  	xmlnsPrefix = "xmlns"
   345  	xmlPrefix   = "xml"
   346  )
   347  
   348  // Apply name space translation to name n.
   349  // The default name space (for Space=="")
   350  // applies only to element names, not to attribute names.
   351  func (d *Decoder) translate(n *Name, isElementName bool) {
   352  	switch {
   353  	case n.Space == xmlnsPrefix:
   354  		return
   355  	case n.Space == "" && !isElementName:
   356  		return
   357  	case n.Space == xmlPrefix:
   358  		n.Space = xmlURL
   359  	case n.Space == "" && n.Local == xmlnsPrefix:
   360  		return
   361  	}
   362  	if v, ok := d.ns[n.Space]; ok {
   363  		n.Space = v
   364  	} else if n.Space == "" {
   365  		n.Space = d.DefaultSpace
   366  	}
   367  }
   368  
   369  func (d *Decoder) switchToReader(r io.Reader) {
   370  	// Get efficient byte at a time reader.
   371  	// Assume that if reader has its own
   372  	// ReadByte, it's efficient enough.
   373  	// Otherwise, use bufio.
   374  	if rb, ok := r.(io.ByteReader); ok {
   375  		d.r = rb
   376  	} else {
   377  		d.r = bufio.NewReader(r)
   378  	}
   379  }
   380  
   381  // Parsing state - stack holds old name space translations
   382  // and the current set of open elements. The translations to pop when
   383  // ending a given tag are *below* it on the stack, which is
   384  // more work but forced on us by XML.
   385  type stack struct {
   386  	next *stack
   387  	kind int
   388  	name Name
   389  	ok   bool
   390  }
   391  
   392  const (
   393  	stkStart = iota
   394  	stkNs
   395  	stkEOF
   396  )
   397  
   398  func (d *Decoder) push(kind int) *stack {
   399  	s := d.free
   400  	if s != nil {
   401  		d.free = s.next
   402  	} else {
   403  		s = new(stack)
   404  	}
   405  	s.next = d.stk
   406  	s.kind = kind
   407  	d.stk = s
   408  	return s
   409  }
   410  
   411  func (d *Decoder) pop() *stack {
   412  	s := d.stk
   413  	if s != nil {
   414  		d.stk = s.next
   415  		s.next = d.free
   416  		d.free = s
   417  	}
   418  	return s
   419  }
   420  
   421  // Record that after the current element is finished
   422  // (that element is already pushed on the stack)
   423  // Token should return EOF until popEOF is called.
   424  func (d *Decoder) pushEOF() {
   425  	// Walk down stack to find Start.
   426  	// It might not be the top, because there might be stkNs
   427  	// entries above it.
   428  	start := d.stk
   429  	for start.kind != stkStart {
   430  		start = start.next
   431  	}
   432  	// The stkNs entries below a start are associated with that
   433  	// element too; skip over them.
   434  	for start.next != nil && start.next.kind == stkNs {
   435  		start = start.next
   436  	}
   437  	s := d.free
   438  	if s != nil {
   439  		d.free = s.next
   440  	} else {
   441  		s = new(stack)
   442  	}
   443  	s.kind = stkEOF
   444  	s.next = start.next
   445  	start.next = s
   446  }
   447  
   448  // Undo a pushEOF.
   449  // The element must have been finished, so the EOF should be at the top of the stack.
   450  func (d *Decoder) popEOF() bool {
   451  	if d.stk == nil || d.stk.kind != stkEOF {
   452  		return false
   453  	}
   454  	d.pop()
   455  	return true
   456  }
   457  
   458  // Record that we are starting an element with the given name.
   459  func (d *Decoder) pushElement(name Name) {
   460  	s := d.push(stkStart)
   461  	s.name = name
   462  }
   463  
   464  // Record that we are changing the value of ns[local].
   465  // The old value is url, ok.
   466  func (d *Decoder) pushNs(local string, url string, ok bool) {
   467  	s := d.push(stkNs)
   468  	s.name.Local = local
   469  	s.name.Space = url
   470  	s.ok = ok
   471  }
   472  
   473  // Creates a SyntaxError with the current line number.
   474  func (d *Decoder) syntaxError(msg string) error {
   475  	return &SyntaxError{Msg: msg, Line: d.line}
   476  }
   477  
   478  // Record that we are ending an element with the given name.
   479  // The name must match the record at the top of the stack,
   480  // which must be a pushElement record.
   481  // After popping the element, apply any undo records from
   482  // the stack to restore the name translations that existed
   483  // before we saw this element.
   484  func (d *Decoder) popElement(t *EndElement) bool {
   485  	s := d.pop()
   486  	name := t.Name
   487  	switch {
   488  	case s == nil || s.kind != stkStart:
   489  		d.err = d.syntaxError("unexpected end element </" + name.Local + ">")
   490  		return false
   491  	case s.name.Local != name.Local:
   492  		if !d.Strict {
   493  			d.needClose = true
   494  			d.toClose = t.Name
   495  			t.Name = s.name
   496  			return true
   497  		}
   498  		d.err = d.syntaxError("element <" + s.name.Local + "> closed by </" + name.Local + ">")
   499  		return false
   500  	case s.name.Space != name.Space:
   501  		d.err = d.syntaxError("element <" + s.name.Local + "> in space " + s.name.Space +
   502  			"closed by </" + name.Local + "> in space " + name.Space)
   503  		return false
   504  	}
   505  
   506  	// Pop stack until a Start or EOF is on the top, undoing the
   507  	// translations that were associated with the element we just closed.
   508  	for d.stk != nil && d.stk.kind != stkStart && d.stk.kind != stkEOF {
   509  		s := d.pop()
   510  		if s.ok {
   511  			d.ns[s.name.Local] = s.name.Space
   512  		} else {
   513  			delete(d.ns, s.name.Local)
   514  		}
   515  	}
   516  
   517  	return true
   518  }
   519  
   520  // If the top element on the stack is autoclosing and
   521  // t is not the end tag, invent the end tag.
   522  func (d *Decoder) autoClose(t Token) (Token, bool) {
   523  	if d.stk == nil || d.stk.kind != stkStart {
   524  		return nil, false
   525  	}
   526  	name := strings.ToLower(d.stk.name.Local)
   527  	for _, s := range d.AutoClose {
   528  		if strings.ToLower(s) == name {
   529  			// This one should be auto closed if t doesn't close it.
   530  			et, ok := t.(EndElement)
   531  			if !ok || et.Name.Local != name {
   532  				return EndElement{d.stk.name}, true
   533  			}
   534  			break
   535  		}
   536  	}
   537  	return nil, false
   538  }
   539  
   540  var errRawToken = errors.New("xml: cannot use RawToken from UnmarshalXML method")
   541  
   542  // RawToken is like Token but does not verify that
   543  // start and end elements match and does not translate
   544  // name space prefixes to their corresponding URLs.
   545  func (d *Decoder) RawToken() (Token, error) {
   546  	if d.unmarshalDepth > 0 {
   547  		return nil, errRawToken
   548  	}
   549  	return d.rawToken()
   550  }
   551  
   552  func (d *Decoder) rawToken() (Token, error) {
   553  	if d.t != nil {
   554  		return d.t.Token()
   555  	}
   556  	if d.err != nil {
   557  		return nil, d.err
   558  	}
   559  	if d.needClose {
   560  		// The last element we read was self-closing and
   561  		// we returned just the StartElement half.
   562  		// Return the EndElement half now.
   563  		d.needClose = false
   564  		return EndElement{d.toClose}, nil
   565  	}
   566  
   567  	b, ok := d.getc()
   568  	if !ok {
   569  		return nil, d.err
   570  	}
   571  
   572  	if b != '<' {
   573  		// Text section.
   574  		d.ungetc(b)
   575  		data := d.text(-1, false)
   576  		if data == nil {
   577  			return nil, d.err
   578  		}
   579  		return CharData(data), nil
   580  	}
   581  
   582  	if b, ok = d.mustgetc(); !ok {
   583  		return nil, d.err
   584  	}
   585  	switch b {
   586  	case '/':
   587  		// </: End element
   588  		var name Name
   589  		if name, ok = d.nsname(); !ok {
   590  			if d.err == nil {
   591  				d.err = d.syntaxError("expected element name after </")
   592  			}
   593  			return nil, d.err
   594  		}
   595  		d.space()
   596  		if b, ok = d.mustgetc(); !ok {
   597  			return nil, d.err
   598  		}
   599  		if b != '>' {
   600  			d.err = d.syntaxError("invalid characters between </" + name.Local + " and >")
   601  			return nil, d.err
   602  		}
   603  		return EndElement{name}, nil
   604  
   605  	case '?':
   606  		// <?: Processing instruction.
   607  		var target string
   608  		if target, ok = d.name(); !ok {
   609  			if d.err == nil {
   610  				d.err = d.syntaxError("expected target name after <?")
   611  			}
   612  			return nil, d.err
   613  		}
   614  		d.space()
   615  		d.buf.Reset()
   616  		var b0 byte
   617  		for {
   618  			if b, ok = d.mustgetc(); !ok {
   619  				return nil, d.err
   620  			}
   621  			d.buf.WriteByte(b)
   622  			if b0 == '?' && b == '>' {
   623  				break
   624  			}
   625  			b0 = b
   626  		}
   627  		data := d.buf.Bytes()
   628  		data = data[0 : len(data)-2] // chop ?>
   629  
   630  		if target == "xml" {
   631  			content := string(data)
   632  			ver := procInst("version", content)
   633  			if ver != "" && ver != "1.0" {
   634  				d.err = fmt.Errorf("xml: unsupported version %q; only version 1.0 is supported", ver)
   635  				return nil, d.err
   636  			}
   637  			enc := procInst("encoding", content)
   638  			if enc != "" && enc != "utf-8" && enc != "UTF-8" && !strings.EqualFold(enc, "utf-8") {
   639  				if d.CharsetReader == nil {
   640  					d.err = fmt.Errorf("xml: encoding %q declared but Decoder.CharsetReader is nil", enc)
   641  					return nil, d.err
   642  				}
   643  				newr, err := d.CharsetReader(enc, d.r.(io.Reader))
   644  				if err != nil {
   645  					d.err = fmt.Errorf("xml: opening charset %q: %v", enc, err)
   646  					return nil, d.err
   647  				}
   648  				if newr == nil {
   649  					panic("CharsetReader returned a nil Reader for charset " + enc)
   650  				}
   651  				d.switchToReader(newr)
   652  			}
   653  		}
   654  		return ProcInst{target, data}, nil
   655  
   656  	case '!':
   657  		// <!: Maybe comment, maybe CDATA.
   658  		if b, ok = d.mustgetc(); !ok {
   659  			return nil, d.err
   660  		}
   661  		switch b {
   662  		case '-': // <!-
   663  			// Probably <!-- for a comment.
   664  			if b, ok = d.mustgetc(); !ok {
   665  				return nil, d.err
   666  			}
   667  			if b != '-' {
   668  				d.err = d.syntaxError("invalid sequence <!- not part of <!--")
   669  				return nil, d.err
   670  			}
   671  			// Look for terminator.
   672  			d.buf.Reset()
   673  			var b0, b1 byte
   674  			for {
   675  				if b, ok = d.mustgetc(); !ok {
   676  					return nil, d.err
   677  				}
   678  				d.buf.WriteByte(b)
   679  				if b0 == '-' && b1 == '-' {
   680  					if b != '>' {
   681  						d.err = d.syntaxError(
   682  							`invalid sequence "--" not allowed in comments`)
   683  						return nil, d.err
   684  					}
   685  					break
   686  				}
   687  				b0, b1 = b1, b
   688  			}
   689  			data := d.buf.Bytes()
   690  			data = data[0 : len(data)-3] // chop -->
   691  			return Comment(data), nil
   692  
   693  		case '[': // <![
   694  			// Probably <![CDATA[.
   695  			for i := 0; i < 6; i++ {
   696  				if b, ok = d.mustgetc(); !ok {
   697  					return nil, d.err
   698  				}
   699  				if b != "CDATA["[i] {
   700  					d.err = d.syntaxError("invalid <![ sequence")
   701  					return nil, d.err
   702  				}
   703  			}
   704  			// Have <![CDATA[.  Read text until ]]>.
   705  			data := d.text(-1, true)
   706  			if data == nil {
   707  				return nil, d.err
   708  			}
   709  			return CharData(data), nil
   710  		}
   711  
   712  		// Probably a directive: <!DOCTYPE ...>, <!ENTITY ...>, etc.
   713  		// We don't care, but accumulate for caller. Quoted angle
   714  		// brackets do not count for nesting.
   715  		d.buf.Reset()
   716  		d.buf.WriteByte(b)
   717  		inquote := uint8(0)
   718  		depth := 0
   719  		for {
   720  			if b, ok = d.mustgetc(); !ok {
   721  				return nil, d.err
   722  			}
   723  			if inquote == 0 && b == '>' && depth == 0 {
   724  				break
   725  			}
   726  		HandleB:
   727  			d.buf.WriteByte(b)
   728  			switch {
   729  			case b == inquote:
   730  				inquote = 0
   731  
   732  			case inquote != 0:
   733  				// in quotes, no special action
   734  
   735  			case b == '\'' || b == '"':
   736  				inquote = b
   737  
   738  			case b == '>' && inquote == 0:
   739  				depth--
   740  
   741  			case b == '<' && inquote == 0:
   742  				// Look for <!-- to begin comment.
   743  				s := "!--"
   744  				for i := 0; i < len(s); i++ {
   745  					if b, ok = d.mustgetc(); !ok {
   746  						return nil, d.err
   747  					}
   748  					if b != s[i] {
   749  						for j := 0; j < i; j++ {
   750  							d.buf.WriteByte(s[j])
   751  						}
   752  						depth++
   753  						goto HandleB
   754  					}
   755  				}
   756  
   757  				// Remove < that was written above.
   758  				d.buf.Truncate(d.buf.Len() - 1)
   759  
   760  				// Look for terminator.
   761  				var b0, b1 byte
   762  				for {
   763  					if b, ok = d.mustgetc(); !ok {
   764  						return nil, d.err
   765  					}
   766  					if b0 == '-' && b1 == '-' && b == '>' {
   767  						break
   768  					}
   769  					b0, b1 = b1, b
   770  				}
   771  			}
   772  		}
   773  		return Directive(d.buf.Bytes()), nil
   774  	}
   775  
   776  	// Must be an open element like <a href="foo">
   777  	d.ungetc(b)
   778  
   779  	var (
   780  		name  Name
   781  		empty bool
   782  		attr  []Attr
   783  	)
   784  	if name, ok = d.nsname(); !ok {
   785  		if d.err == nil {
   786  			d.err = d.syntaxError("expected element name after <")
   787  		}
   788  		return nil, d.err
   789  	}
   790  
   791  	attr = []Attr{}
   792  	for {
   793  		d.space()
   794  		if b, ok = d.mustgetc(); !ok {
   795  			return nil, d.err
   796  		}
   797  		if b == '/' {
   798  			empty = true
   799  			if b, ok = d.mustgetc(); !ok {
   800  				return nil, d.err
   801  			}
   802  			if b != '>' {
   803  				d.err = d.syntaxError("expected /> in element")
   804  				return nil, d.err
   805  			}
   806  			break
   807  		}
   808  		if b == '>' {
   809  			break
   810  		}
   811  		d.ungetc(b)
   812  
   813  		a := Attr{}
   814  		if a.Name, ok = d.nsname(); !ok {
   815  			if d.err == nil {
   816  				d.err = d.syntaxError("expected attribute name in element")
   817  			}
   818  			return nil, d.err
   819  		}
   820  		d.space()
   821  		if b, ok = d.mustgetc(); !ok {
   822  			return nil, d.err
   823  		}
   824  		if b != '=' {
   825  			if d.Strict {
   826  				d.err = d.syntaxError("attribute name without = in element")
   827  				return nil, d.err
   828  			}
   829  			d.ungetc(b)
   830  			a.Value = a.Name.Local
   831  		} else {
   832  			d.space()
   833  			data := d.attrval()
   834  			if data == nil {
   835  				return nil, d.err
   836  			}
   837  			a.Value = string(data)
   838  		}
   839  		attr = append(attr, a)
   840  	}
   841  	if empty {
   842  		d.needClose = true
   843  		d.toClose = name
   844  	}
   845  	return StartElement{name, attr}, nil
   846  }
   847  
   848  func (d *Decoder) attrval() []byte {
   849  	b, ok := d.mustgetc()
   850  	if !ok {
   851  		return nil
   852  	}
   853  	// Handle quoted attribute values
   854  	if b == '"' || b == '\'' {
   855  		return d.text(int(b), false)
   856  	}
   857  	// Handle unquoted attribute values for strict parsers
   858  	if d.Strict {
   859  		d.err = d.syntaxError("unquoted or missing attribute value in element")
   860  		return nil
   861  	}
   862  	// Handle unquoted attribute values for unstrict parsers
   863  	d.ungetc(b)
   864  	d.buf.Reset()
   865  	for {
   866  		b, ok = d.mustgetc()
   867  		if !ok {
   868  			return nil
   869  		}
   870  		// https://www.w3.org/TR/REC-html40/intro/sgmltut.html#h-3.2.2
   871  		if 'a' <= b && b <= 'z' || 'A' <= b && b <= 'Z' ||
   872  			'0' <= b && b <= '9' || b == '_' || b == ':' || b == '-' {
   873  			d.buf.WriteByte(b)
   874  		} else {
   875  			d.ungetc(b)
   876  			break
   877  		}
   878  	}
   879  	return d.buf.Bytes()
   880  }
   881  
   882  // Skip spaces if any
   883  func (d *Decoder) space() {
   884  	for {
   885  		b, ok := d.getc()
   886  		if !ok {
   887  			return
   888  		}
   889  		switch b {
   890  		case ' ', '\r', '\n', '\t':
   891  		default:
   892  			d.ungetc(b)
   893  			return
   894  		}
   895  	}
   896  }
   897  
   898  // Read a single byte.
   899  // If there is no byte to read, return ok==false
   900  // and leave the error in d.err.
   901  // Maintain line number.
   902  func (d *Decoder) getc() (b byte, ok bool) {
   903  	if d.err != nil {
   904  		return 0, false
   905  	}
   906  	if d.nextByte >= 0 {
   907  		b = byte(d.nextByte)
   908  		d.nextByte = -1
   909  	} else {
   910  		b, d.err = d.r.ReadByte()
   911  		if d.err != nil {
   912  			return 0, false
   913  		}
   914  		if d.saved != nil {
   915  			d.saved.WriteByte(b)
   916  		}
   917  	}
   918  	if b == '\n' {
   919  		d.line++
   920  	}
   921  	d.offset++
   922  	return b, true
   923  }
   924  
   925  // InputOffset returns the input stream byte offset of the current decoder position.
   926  // The offset gives the location of the end of the most recently returned token
   927  // and the beginning of the next token.
   928  func (d *Decoder) InputOffset() int64 {
   929  	return d.offset
   930  }
   931  
   932  // Return saved offset.
   933  // If we did ungetc (nextByte >= 0), have to back up one.
   934  func (d *Decoder) savedOffset() int {
   935  	n := d.saved.Len()
   936  	if d.nextByte >= 0 {
   937  		n--
   938  	}
   939  	return n
   940  }
   941  
   942  // Must read a single byte.
   943  // If there is no byte to read,
   944  // set d.err to SyntaxError("unexpected EOF")
   945  // and return ok==false
   946  func (d *Decoder) mustgetc() (b byte, ok bool) {
   947  	if b, ok = d.getc(); !ok {
   948  		if d.err == io.EOF {
   949  			d.err = d.syntaxError("unexpected EOF")
   950  		}
   951  	}
   952  	return
   953  }
   954  
   955  // Unread a single byte.
   956  func (d *Decoder) ungetc(b byte) {
   957  	if b == '\n' {
   958  		d.line--
   959  	}
   960  	d.nextByte = int(b)
   961  	d.offset--
   962  }
   963  
   964  var entity = map[string]rune{
   965  	"lt":   '<',
   966  	"gt":   '>',
   967  	"amp":  '&',
   968  	"apos": '\'',
   969  	"quot": '"',
   970  }
   971  
   972  // Read plain text section (XML calls it character data).
   973  // If quote >= 0, we are in a quoted string and need to find the matching quote.
   974  // If cdata == true, we are in a <![CDATA[ section and need to find ]]>.
   975  // On failure return nil and leave the error in d.err.
   976  func (d *Decoder) text(quote int, cdata bool) []byte {
   977  	var b0, b1 byte
   978  	var trunc int
   979  	d.buf.Reset()
   980  Input:
   981  	for {
   982  		b, ok := d.getc()
   983  		if !ok {
   984  			if cdata {
   985  				if d.err == io.EOF {
   986  					d.err = d.syntaxError("unexpected EOF in CDATA section")
   987  				}
   988  				return nil
   989  			}
   990  			break Input
   991  		}
   992  
   993  		// <![CDATA[ section ends with ]]>.
   994  		// It is an error for ]]> to appear in ordinary text.
   995  		if b0 == ']' && b1 == ']' && b == '>' {
   996  			if cdata {
   997  				trunc = 2
   998  				break Input
   999  			}
  1000  			d.err = d.syntaxError("unescaped ]]> not in CDATA section")
  1001  			return nil
  1002  		}
  1003  
  1004  		// Stop reading text if we see a <.
  1005  		if b == '<' && !cdata {
  1006  			if quote >= 0 {
  1007  				d.err = d.syntaxError("unescaped < inside quoted string")
  1008  				return nil
  1009  			}
  1010  			d.ungetc('<')
  1011  			break Input
  1012  		}
  1013  		if quote >= 0 && b == byte(quote) {
  1014  			break Input
  1015  		}
  1016  		if b == '&' && !cdata {
  1017  			// Read escaped character expression up to semicolon.
  1018  			// XML in all its glory allows a document to define and use
  1019  			// its own character names with <!ENTITY ...> directives.
  1020  			// Parsers are required to recognize lt, gt, amp, apos, and quot
  1021  			// even if they have not been declared.
  1022  			before := d.buf.Len()
  1023  			d.buf.WriteByte('&')
  1024  			var ok bool
  1025  			var text string
  1026  			var haveText bool
  1027  			if b, ok = d.mustgetc(); !ok {
  1028  				return nil
  1029  			}
  1030  			if b == '#' {
  1031  				d.buf.WriteByte(b)
  1032  				if b, ok = d.mustgetc(); !ok {
  1033  					return nil
  1034  				}
  1035  				base := 10
  1036  				if b == 'x' {
  1037  					base = 16
  1038  					d.buf.WriteByte(b)
  1039  					if b, ok = d.mustgetc(); !ok {
  1040  						return nil
  1041  					}
  1042  				}
  1043  				start := d.buf.Len()
  1044  				for '0' <= b && b <= '9' ||
  1045  					base == 16 && 'a' <= b && b <= 'f' ||
  1046  					base == 16 && 'A' <= b && b <= 'F' {
  1047  					d.buf.WriteByte(b)
  1048  					if b, ok = d.mustgetc(); !ok {
  1049  						return nil
  1050  					}
  1051  				}
  1052  				if b != ';' {
  1053  					d.ungetc(b)
  1054  				} else {
  1055  					s := string(d.buf.Bytes()[start:])
  1056  					d.buf.WriteByte(';')
  1057  					n, err := strconv.ParseUint(s, base, 64)
  1058  					if err == nil && n <= unicode.MaxRune {
  1059  						text = string(rune(n))
  1060  						haveText = true
  1061  					}
  1062  				}
  1063  			} else {
  1064  				d.ungetc(b)
  1065  				if !d.readName() {
  1066  					if d.err != nil {
  1067  						return nil
  1068  					}
  1069  				}
  1070  				if b, ok = d.mustgetc(); !ok {
  1071  					return nil
  1072  				}
  1073  				if b != ';' {
  1074  					d.ungetc(b)
  1075  				} else {
  1076  					name := d.buf.Bytes()[before+1:]
  1077  					d.buf.WriteByte(';')
  1078  					if isName(name) {
  1079  						s := string(name)
  1080  						if r, ok := entity[s]; ok {
  1081  							text = string(r)
  1082  							haveText = true
  1083  						} else if d.Entity != nil {
  1084  							text, haveText = d.Entity[s]
  1085  						}
  1086  					}
  1087  				}
  1088  			}
  1089  
  1090  			if haveText {
  1091  				d.buf.Truncate(before)
  1092  				d.buf.Write([]byte(text))
  1093  				b0, b1 = 0, 0
  1094  				continue Input
  1095  			}
  1096  			if !d.Strict {
  1097  				b0, b1 = 0, 0
  1098  				continue Input
  1099  			}
  1100  			ent := string(d.buf.Bytes()[before:])
  1101  			if ent[len(ent)-1] != ';' {
  1102  				ent += " (no semicolon)"
  1103  			}
  1104  			d.err = d.syntaxError("invalid character entity " + ent)
  1105  			return nil
  1106  		}
  1107  
  1108  		// We must rewrite unescaped \r and \r\n into \n.
  1109  		if b == '\r' {
  1110  			d.buf.WriteByte('\n')
  1111  		} else if b1 == '\r' && b == '\n' {
  1112  			// Skip \r\n--we already wrote \n.
  1113  		} else {
  1114  			d.buf.WriteByte(b)
  1115  		}
  1116  
  1117  		b0, b1 = b1, b
  1118  	}
  1119  	data := d.buf.Bytes()
  1120  	data = data[0 : len(data)-trunc]
  1121  
  1122  	// Inspect each rune for being a disallowed character.
  1123  	buf := data
  1124  	for len(buf) > 0 {
  1125  		r, size := utf8.DecodeRune(buf)
  1126  		if r == utf8.RuneError && size == 1 {
  1127  			d.err = d.syntaxError("invalid UTF-8")
  1128  			return nil
  1129  		}
  1130  		buf = buf[size:]
  1131  		if !isInCharacterRange(r) {
  1132  			d.err = d.syntaxError(fmt.Sprintf("illegal character code %U", r))
  1133  			return nil
  1134  		}
  1135  	}
  1136  
  1137  	return data
  1138  }
  1139  
  1140  // Decide whether the given rune is in the XML Character Range, per
  1141  // the Char production of https://www.xml.com/axml/testaxml.htm,
  1142  // Section 2.2 Characters.
  1143  func isInCharacterRange(r rune) (inrange bool) {
  1144  	return r == 0x09 ||
  1145  		r == 0x0A ||
  1146  		r == 0x0D ||
  1147  		r >= 0x20 && r <= 0xD7FF ||
  1148  		r >= 0xE000 && r <= 0xFFFD ||
  1149  		r >= 0x10000 && r <= 0x10FFFF
  1150  }
  1151  
  1152  // Get name space name: name with a : stuck in the middle.
  1153  // The part before the : is the name space identifier.
  1154  func (d *Decoder) nsname() (name Name, ok bool) {
  1155  	s, ok := d.name()
  1156  	if !ok {
  1157  		return
  1158  	}
  1159  	i := strings.Index(s, ":")
  1160  	if i < 0 {
  1161  		name.Local = s
  1162  	} else {
  1163  		name.Space = s[0:i]
  1164  		name.Local = s[i+1:]
  1165  	}
  1166  	return name, true
  1167  }
  1168  
  1169  // Get name: /first(first|second)*/
  1170  // Do not set d.err if the name is missing (unless unexpected EOF is received):
  1171  // let the caller provide better context.
  1172  func (d *Decoder) name() (s string, ok bool) {
  1173  	d.buf.Reset()
  1174  	if !d.readName() {
  1175  		return "", false
  1176  	}
  1177  
  1178  	// Now we check the characters.
  1179  	b := d.buf.Bytes()
  1180  	if !isName(b) {
  1181  		d.err = d.syntaxError("invalid XML name: " + string(b))
  1182  		return "", false
  1183  	}
  1184  	return string(b), true
  1185  }
  1186  
  1187  // Read a name and append its bytes to d.buf.
  1188  // The name is delimited by any single-byte character not valid in names.
  1189  // All multi-byte characters are accepted; the caller must check their validity.
  1190  func (d *Decoder) readName() (ok bool) {
  1191  	var b byte
  1192  	if b, ok = d.mustgetc(); !ok {
  1193  		return
  1194  	}
  1195  	if b < utf8.RuneSelf && !isNameByte(b) {
  1196  		d.ungetc(b)
  1197  		return false
  1198  	}
  1199  	d.buf.WriteByte(b)
  1200  
  1201  	for {
  1202  		if b, ok = d.mustgetc(); !ok {
  1203  			return
  1204  		}
  1205  		if b < utf8.RuneSelf && !isNameByte(b) {
  1206  			d.ungetc(b)
  1207  			break
  1208  		}
  1209  		d.buf.WriteByte(b)
  1210  	}
  1211  	return true
  1212  }
  1213  
  1214  func isNameByte(c byte) bool {
  1215  	return 'A' <= c && c <= 'Z' ||
  1216  		'a' <= c && c <= 'z' ||
  1217  		'0' <= c && c <= '9' ||
  1218  		c == '_' || c == ':' || c == '.' || c == '-'
  1219  }
  1220  
  1221  func isName(s []byte) bool {
  1222  	if len(s) == 0 {
  1223  		return false
  1224  	}
  1225  	c, n := utf8.DecodeRune(s)
  1226  	if c == utf8.RuneError && n == 1 {
  1227  		return false
  1228  	}
  1229  	if !unicode.Is(first, c) {
  1230  		return false
  1231  	}
  1232  	for n < len(s) {
  1233  		s = s[n:]
  1234  		c, n = utf8.DecodeRune(s)
  1235  		if c == utf8.RuneError && n == 1 {
  1236  			return false
  1237  		}
  1238  		if !unicode.Is(first, c) && !unicode.Is(second, c) {
  1239  			return false
  1240  		}
  1241  	}
  1242  	return true
  1243  }
  1244  
  1245  func isNameString(s string) bool {
  1246  	if len(s) == 0 {
  1247  		return false
  1248  	}
  1249  	c, n := utf8.DecodeRuneInString(s)
  1250  	if c == utf8.RuneError && n == 1 {
  1251  		return false
  1252  	}
  1253  	if !unicode.Is(first, c) {
  1254  		return false
  1255  	}
  1256  	for n < len(s) {
  1257  		s = s[n:]
  1258  		c, n = utf8.DecodeRuneInString(s)
  1259  		if c == utf8.RuneError && n == 1 {
  1260  			return false
  1261  		}
  1262  		if !unicode.Is(first, c) && !unicode.Is(second, c) {
  1263  			return false
  1264  		}
  1265  	}
  1266  	return true
  1267  }
  1268  
  1269  // These tables were generated by cut and paste from Appendix B of
  1270  // the XML spec at https://www.xml.com/axml/testaxml.htm
  1271  // and then reformatting. First corresponds to (Letter | '_' | ':')
  1272  // and second corresponds to NameChar.
  1273  
  1274  var first = &unicode.RangeTable{
  1275  	R16: []unicode.Range16{
  1276  		{0x003A, 0x003A, 1},
  1277  		{0x0041, 0x005A, 1},
  1278  		{0x005F, 0x005F, 1},
  1279  		{0x0061, 0x007A, 1},
  1280  		{0x00C0, 0x00D6, 1},
  1281  		{0x00D8, 0x00F6, 1},
  1282  		{0x00F8, 0x00FF, 1},
  1283  		{0x0100, 0x0131, 1},
  1284  		{0x0134, 0x013E, 1},
  1285  		{0x0141, 0x0148, 1},
  1286  		{0x014A, 0x017E, 1},
  1287  		{0x0180, 0x01C3, 1},
  1288  		{0x01CD, 0x01F0, 1},
  1289  		{0x01F4, 0x01F5, 1},
  1290  		{0x01FA, 0x0217, 1},
  1291  		{0x0250, 0x02A8, 1},
  1292  		{0x02BB, 0x02C1, 1},
  1293  		{0x0386, 0x0386, 1},
  1294  		{0x0388, 0x038A, 1},
  1295  		{0x038C, 0x038C, 1},
  1296  		{0x038E, 0x03A1, 1},
  1297  		{0x03A3, 0x03CE, 1},
  1298  		{0x03D0, 0x03D6, 1},
  1299  		{0x03DA, 0x03E0, 2},
  1300  		{0x03E2, 0x03F3, 1},
  1301  		{0x0401, 0x040C, 1},
  1302  		{0x040E, 0x044F, 1},
  1303  		{0x0451, 0x045C, 1},
  1304  		{0x045E, 0x0481, 1},
  1305  		{0x0490, 0x04C4, 1},
  1306  		{0x04C7, 0x04C8, 1},
  1307  		{0x04CB, 0x04CC, 1},
  1308  		{0x04D0, 0x04EB, 1},
  1309  		{0x04EE, 0x04F5, 1},
  1310  		{0x04F8, 0x04F9, 1},
  1311  		{0x0531, 0x0556, 1},
  1312  		{0x0559, 0x0559, 1},
  1313  		{0x0561, 0x0586, 1},
  1314  		{0x05D0, 0x05EA, 1},
  1315  		{0x05F0, 0x05F2, 1},
  1316  		{0x0621, 0x063A, 1},
  1317  		{0x0641, 0x064A, 1},
  1318  		{0x0671, 0x06B7, 1},
  1319  		{0x06BA, 0x06BE, 1},
  1320  		{0x06C0, 0x06CE, 1},
  1321  		{0x06D0, 0x06D3, 1},
  1322  		{0x06D5, 0x06D5, 1},
  1323  		{0x06E5, 0x06E6, 1},
  1324  		{0x0905, 0x0939, 1},
  1325  		{0x093D, 0x093D, 1},
  1326  		{0x0958, 0x0961, 1},
  1327  		{0x0985, 0x098C, 1},
  1328  		{0x098F, 0x0990, 1},
  1329  		{0x0993, 0x09A8, 1},
  1330  		{0x09AA, 0x09B0, 1},
  1331  		{0x09B2, 0x09B2, 1},
  1332  		{0x09B6, 0x09B9, 1},
  1333  		{0x09DC, 0x09DD, 1},
  1334  		{0x09DF, 0x09E1, 1},
  1335  		{0x09F0, 0x09F1, 1},
  1336  		{0x0A05, 0x0A0A, 1},
  1337  		{0x0A0F, 0x0A10, 1},
  1338  		{0x0A13, 0x0A28, 1},
  1339  		{0x0A2A, 0x0A30, 1},
  1340  		{0x0A32, 0x0A33, 1},
  1341  		{0x0A35, 0x0A36, 1},
  1342  		{0x0A38, 0x0A39, 1},
  1343  		{0x0A59, 0x0A5C, 1},
  1344  		{0x0A5E, 0x0A5E, 1},
  1345  		{0x0A72, 0x0A74, 1},
  1346  		{0x0A85, 0x0A8B, 1},
  1347  		{0x0A8D, 0x0A8D, 1},
  1348  		{0x0A8F, 0x0A91, 1},
  1349  		{0x0A93, 0x0AA8, 1},
  1350  		{0x0AAA, 0x0AB0, 1},
  1351  		{0x0AB2, 0x0AB3, 1},
  1352  		{0x0AB5, 0x0AB9, 1},
  1353  		{0x0ABD, 0x0AE0, 0x23},
  1354  		{0x0B05, 0x0B0C, 1},
  1355  		{0x0B0F, 0x0B10, 1},
  1356  		{0x0B13, 0x0B28, 1},
  1357  		{0x0B2A, 0x0B30, 1},
  1358  		{0x0B32, 0x0B33, 1},
  1359  		{0x0B36, 0x0B39, 1},
  1360  		{0x0B3D, 0x0B3D, 1},
  1361  		{0x0B5C, 0x0B5D, 1},
  1362  		{0x0B5F, 0x0B61, 1},
  1363  		{0x0B85, 0x0B8A, 1},
  1364  		{0x0B8E, 0x0B90, 1},
  1365  		{0x0B92, 0x0B95, 1},
  1366  		{0x0B99, 0x0B9A, 1},
  1367  		{0x0B9C, 0x0B9C, 1},
  1368  		{0x0B9E, 0x0B9F, 1},
  1369  		{0x0BA3, 0x0BA4, 1},
  1370  		{0x0BA8, 0x0BAA, 1},
  1371  		{0x0BAE, 0x0BB5, 1},
  1372  		{0x0BB7, 0x0BB9, 1},
  1373  		{0x0C05, 0x0C0C, 1},
  1374  		{0x0C0E, 0x0C10, 1},
  1375  		{0x0C12, 0x0C28, 1},
  1376  		{0x0C2A, 0x0C33, 1},
  1377  		{0x0C35, 0x0C39, 1},
  1378  		{0x0C60, 0x0C61, 1},
  1379  		{0x0C85, 0x0C8C, 1},
  1380  		{0x0C8E, 0x0C90, 1},
  1381  		{0x0C92, 0x0CA8, 1},
  1382  		{0x0CAA, 0x0CB3, 1},
  1383  		{0x0CB5, 0x0CB9, 1},
  1384  		{0x0CDE, 0x0CDE, 1},
  1385  		{0x0CE0, 0x0CE1, 1},
  1386  		{0x0D05, 0x0D0C, 1},
  1387  		{0x0D0E, 0x0D10, 1},
  1388  		{0x0D12, 0x0D28, 1},
  1389  		{0x0D2A, 0x0D39, 1},
  1390  		{0x0D60, 0x0D61, 1},
  1391  		{0x0E01, 0x0E2E, 1},
  1392  		{0x0E30, 0x0E30, 1},
  1393  		{0x0E32, 0x0E33, 1},
  1394  		{0x0E40, 0x0E45, 1},
  1395  		{0x0E81, 0x0E82, 1},
  1396  		{0x0E84, 0x0E84, 1},
  1397  		{0x0E87, 0x0E88, 1},
  1398  		{0x0E8A, 0x0E8D, 3},
  1399  		{0x0E94, 0x0E97, 1},
  1400  		{0x0E99, 0x0E9F, 1},
  1401  		{0x0EA1, 0x0EA3, 1},
  1402  		{0x0EA5, 0x0EA7, 2},
  1403  		{0x0EAA, 0x0EAB, 1},
  1404  		{0x0EAD, 0x0EAE, 1},
  1405  		{0x0EB0, 0x0EB0, 1},
  1406  		{0x0EB2, 0x0EB3, 1},
  1407  		{0x0EBD, 0x0EBD, 1},
  1408  		{0x0EC0, 0x0EC4, 1},
  1409  		{0x0F40, 0x0F47, 1},
  1410  		{0x0F49, 0x0F69, 1},
  1411  		{0x10A0, 0x10C5, 1},
  1412  		{0x10D0, 0x10F6, 1},
  1413  		{0x1100, 0x1100, 1},
  1414  		{0x1102, 0x1103, 1},
  1415  		{0x1105, 0x1107, 1},
  1416  		{0x1109, 0x1109, 1},
  1417  		{0x110B, 0x110C, 1},
  1418  		{0x110E, 0x1112, 1},
  1419  		{0x113C, 0x1140, 2},
  1420  		{0x114C, 0x1150, 2},
  1421  		{0x1154, 0x1155, 1},
  1422  		{0x1159, 0x1159, 1},
  1423  		{0x115F, 0x1161, 1},
  1424  		{0x1163, 0x1169, 2},
  1425  		{0x116D, 0x116E, 1},
  1426  		{0x1172, 0x1173, 1},
  1427  		{0x1175, 0x119E, 0x119E - 0x1175},
  1428  		{0x11A8, 0x11AB, 0x11AB - 0x11A8},
  1429  		{0x11AE, 0x11AF, 1},
  1430  		{0x11B7, 0x11B8, 1},
  1431  		{0x11BA, 0x11BA, 1},
  1432  		{0x11BC, 0x11C2, 1},
  1433  		{0x11EB, 0x11F0, 0x11F0 - 0x11EB},
  1434  		{0x11F9, 0x11F9, 1},
  1435  		{0x1E00, 0x1E9B, 1},
  1436  		{0x1EA0, 0x1EF9, 1},
  1437  		{0x1F00, 0x1F15, 1},
  1438  		{0x1F18, 0x1F1D, 1},
  1439  		{0x1F20, 0x1F45, 1},
  1440  		{0x1F48, 0x1F4D, 1},
  1441  		{0x1F50, 0x1F57, 1},
  1442  		{0x1F59, 0x1F5B, 0x1F5B - 0x1F59},
  1443  		{0x1F5D, 0x1F5D, 1},
  1444  		{0x1F5F, 0x1F7D, 1},
  1445  		{0x1F80, 0x1FB4, 1},
  1446  		{0x1FB6, 0x1FBC, 1},
  1447  		{0x1FBE, 0x1FBE, 1},
  1448  		{0x1FC2, 0x1FC4, 1},
  1449  		{0x1FC6, 0x1FCC, 1},
  1450  		{0x1FD0, 0x1FD3, 1},
  1451  		{0x1FD6, 0x1FDB, 1},
  1452  		{0x1FE0, 0x1FEC, 1},
  1453  		{0x1FF2, 0x1FF4, 1},
  1454  		{0x1FF6, 0x1FFC, 1},
  1455  		{0x2126, 0x2126, 1},
  1456  		{0x212A, 0x212B, 1},
  1457  		{0x212E, 0x212E, 1},
  1458  		{0x2180, 0x2182, 1},
  1459  		{0x3007, 0x3007, 1},
  1460  		{0x3021, 0x3029, 1},
  1461  		{0x3041, 0x3094, 1},
  1462  		{0x30A1, 0x30FA, 1},
  1463  		{0x3105, 0x312C, 1},
  1464  		{0x4E00, 0x9FA5, 1},
  1465  		{0xAC00, 0xD7A3, 1},
  1466  	},
  1467  }
  1468  
  1469  var second = &unicode.RangeTable{
  1470  	R16: []unicode.Range16{
  1471  		{0x002D, 0x002E, 1},
  1472  		{0x0030, 0x0039, 1},
  1473  		{0x00B7, 0x00B7, 1},
  1474  		{0x02D0, 0x02D1, 1},
  1475  		{0x0300, 0x0345, 1},
  1476  		{0x0360, 0x0361, 1},
  1477  		{0x0387, 0x0387, 1},
  1478  		{0x0483, 0x0486, 1},
  1479  		{0x0591, 0x05A1, 1},
  1480  		{0x05A3, 0x05B9, 1},
  1481  		{0x05BB, 0x05BD, 1},
  1482  		{0x05BF, 0x05BF, 1},
  1483  		{0x05C1, 0x05C2, 1},
  1484  		{0x05C4, 0x0640, 0x0640 - 0x05C4},
  1485  		{0x064B, 0x0652, 1},
  1486  		{0x0660, 0x0669, 1},
  1487  		{0x0670, 0x0670, 1},
  1488  		{0x06D6, 0x06DC, 1},
  1489  		{0x06DD, 0x06DF, 1},
  1490  		{0x06E0, 0x06E4, 1},
  1491  		{0x06E7, 0x06E8, 1},
  1492  		{0x06EA, 0x06ED, 1},
  1493  		{0x06F0, 0x06F9, 1},
  1494  		{0x0901, 0x0903, 1},
  1495  		{0x093C, 0x093C, 1},
  1496  		{0x093E, 0x094C, 1},
  1497  		{0x094D, 0x094D, 1},
  1498  		{0x0951, 0x0954, 1},
  1499  		{0x0962, 0x0963, 1},
  1500  		{0x0966, 0x096F, 1},
  1501  		{0x0981, 0x0983, 1},
  1502  		{0x09BC, 0x09BC, 1},
  1503  		{0x09BE, 0x09BF, 1},
  1504  		{0x09C0, 0x09C4, 1},
  1505  		{0x09C7, 0x09C8, 1},
  1506  		{0x09CB, 0x09CD, 1},
  1507  		{0x09D7, 0x09D7, 1},
  1508  		{0x09E2, 0x09E3, 1},
  1509  		{0x09E6, 0x09EF, 1},
  1510  		{0x0A02, 0x0A3C, 0x3A},
  1511  		{0x0A3E, 0x0A3F, 1},
  1512  		{0x0A40, 0x0A42, 1},
  1513  		{0x0A47, 0x0A48, 1},
  1514  		{0x0A4B, 0x0A4D, 1},
  1515  		{0x0A66, 0x0A6F, 1},
  1516  		{0x0A70, 0x0A71, 1},
  1517  		{0x0A81, 0x0A83, 1},
  1518  		{0x0ABC, 0x0ABC, 1},
  1519  		{0x0ABE, 0x0AC5, 1},
  1520  		{0x0AC7, 0x0AC9, 1},
  1521  		{0x0ACB, 0x0ACD, 1},
  1522  		{0x0AE6, 0x0AEF, 1},
  1523  		{0x0B01, 0x0B03, 1},
  1524  		{0x0B3C, 0x0B3C, 1},
  1525  		{0x0B3E, 0x0B43, 1},
  1526  		{0x0B47, 0x0B48, 1},
  1527  		{0x0B4B, 0x0B4D, 1},
  1528  		{0x0B56, 0x0B57, 1},
  1529  		{0x0B66, 0x0B6F, 1},
  1530  		{0x0B82, 0x0B83, 1},
  1531  		{0x0BBE, 0x0BC2, 1},
  1532  		{0x0BC6, 0x0BC8, 1},
  1533  		{0x0BCA, 0x0BCD, 1},
  1534  		{0x0BD7, 0x0BD7, 1},
  1535  		{0x0BE7, 0x0BEF, 1},
  1536  		{0x0C01, 0x0C03, 1},
  1537  		{0x0C3E, 0x0C44, 1},
  1538  		{0x0C46, 0x0C48, 1},
  1539  		{0x0C4A, 0x0C4D, 1},
  1540  		{0x0C55, 0x0C56, 1},
  1541  		{0x0C66, 0x0C6F, 1},
  1542  		{0x0C82, 0x0C83, 1},
  1543  		{0x0CBE, 0x0CC4, 1},
  1544  		{0x0CC6, 0x0CC8, 1},
  1545  		{0x0CCA, 0x0CCD, 1},
  1546  		{0x0CD5, 0x0CD6, 1},
  1547  		{0x0CE6, 0x0CEF, 1},
  1548  		{0x0D02, 0x0D03, 1},
  1549  		{0x0D3E, 0x0D43, 1},
  1550  		{0x0D46, 0x0D48, 1},
  1551  		{0x0D4A, 0x0D4D, 1},
  1552  		{0x0D57, 0x0D57, 1},
  1553  		{0x0D66, 0x0D6F, 1},
  1554  		{0x0E31, 0x0E31, 1},
  1555  		{0x0E34, 0x0E3A, 1},
  1556  		{0x0E46, 0x0E46, 1},
  1557  		{0x0E47, 0x0E4E, 1},
  1558  		{0x0E50, 0x0E59, 1},
  1559  		{0x0EB1, 0x0EB1, 1},
  1560  		{0x0EB4, 0x0EB9, 1},
  1561  		{0x0EBB, 0x0EBC, 1},
  1562  		{0x0EC6, 0x0EC6, 1},
  1563  		{0x0EC8, 0x0ECD, 1},
  1564  		{0x0ED0, 0x0ED9, 1},
  1565  		{0x0F18, 0x0F19, 1},
  1566  		{0x0F20, 0x0F29, 1},
  1567  		{0x0F35, 0x0F39, 2},
  1568  		{0x0F3E, 0x0F3F, 1},
  1569  		{0x0F71, 0x0F84, 1},
  1570  		{0x0F86, 0x0F8B, 1},
  1571  		{0x0F90, 0x0F95, 1},
  1572  		{0x0F97, 0x0F97, 1},
  1573  		{0x0F99, 0x0FAD, 1},
  1574  		{0x0FB1, 0x0FB7, 1},
  1575  		{0x0FB9, 0x0FB9, 1},
  1576  		{0x20D0, 0x20DC, 1},
  1577  		{0x20E1, 0x3005, 0x3005 - 0x20E1},
  1578  		{0x302A, 0x302F, 1},
  1579  		{0x3031, 0x3035, 1},
  1580  		{0x3099, 0x309A, 1},
  1581  		{0x309D, 0x309E, 1},
  1582  		{0x30FC, 0x30FE, 1},
  1583  	},
  1584  }
  1585  
  1586  // HTMLEntity is an entity map containing translations for the
  1587  // standard HTML entity characters.
  1588  //
  1589  // See the Decoder.Strict and Decoder.Entity fields' documentation.
  1590  var HTMLEntity map[string]string = htmlEntity
  1591  
  1592  var htmlEntity = map[string]string{
  1593  	/*
  1594  		hget http://www.w3.org/TR/html4/sgml/entities.html |
  1595  		ssam '
  1596  			,y /\&gt;/ x/\&lt;(.|\n)+/ s/\n/ /g
  1597  			,x v/^\&lt;!ENTITY/d
  1598  			,s/\&lt;!ENTITY ([^ ]+) .*U\+([0-9A-F][0-9A-F][0-9A-F][0-9A-F]) .+/	"\1": "\\u\2",/g
  1599  		'
  1600  	*/
  1601  	"nbsp":     "\u00A0",
  1602  	"iexcl":    "\u00A1",
  1603  	"cent":     "\u00A2",
  1604  	"pound":    "\u00A3",
  1605  	"curren":   "\u00A4",
  1606  	"yen":      "\u00A5",
  1607  	"brvbar":   "\u00A6",
  1608  	"sect":     "\u00A7",
  1609  	"uml":      "\u00A8",
  1610  	"copy":     "\u00A9",
  1611  	"ordf":     "\u00AA",
  1612  	"laquo":    "\u00AB",
  1613  	"not":      "\u00AC",
  1614  	"shy":      "\u00AD",
  1615  	"reg":      "\u00AE",
  1616  	"macr":     "\u00AF",
  1617  	"deg":      "\u00B0",
  1618  	"plusmn":   "\u00B1",
  1619  	"sup2":     "\u00B2",
  1620  	"sup3":     "\u00B3",
  1621  	"acute":    "\u00B4",
  1622  	"micro":    "\u00B5",
  1623  	"para":     "\u00B6",
  1624  	"middot":   "\u00B7",
  1625  	"cedil":    "\u00B8",
  1626  	"sup1":     "\u00B9",
  1627  	"ordm":     "\u00BA",
  1628  	"raquo":    "\u00BB",
  1629  	"frac14":   "\u00BC",
  1630  	"frac12":   "\u00BD",
  1631  	"frac34":   "\u00BE",
  1632  	"iquest":   "\u00BF",
  1633  	"Agrave":   "\u00C0",
  1634  	"Aacute":   "\u00C1",
  1635  	"Acirc":    "\u00C2",
  1636  	"Atilde":   "\u00C3",
  1637  	"Auml":     "\u00C4",
  1638  	"Aring":    "\u00C5",
  1639  	"AElig":    "\u00C6",
  1640  	"Ccedil":   "\u00C7",
  1641  	"Egrave":   "\u00C8",
  1642  	"Eacute":   "\u00C9",
  1643  	"Ecirc":    "\u00CA",
  1644  	"Euml":     "\u00CB",
  1645  	"Igrave":   "\u00CC",
  1646  	"Iacute":   "\u00CD",
  1647  	"Icirc":    "\u00CE",
  1648  	"Iuml":     "\u00CF",
  1649  	"ETH":      "\u00D0",
  1650  	"Ntilde":   "\u00D1",
  1651  	"Ograve":   "\u00D2",
  1652  	"Oacute":   "\u00D3",
  1653  	"Ocirc":    "\u00D4",
  1654  	"Otilde":   "\u00D5",
  1655  	"Ouml":     "\u00D6",
  1656  	"times":    "\u00D7",
  1657  	"Oslash":   "\u00D8",
  1658  	"Ugrave":   "\u00D9",
  1659  	"Uacute":   "\u00DA",
  1660  	"Ucirc":    "\u00DB",
  1661  	"Uuml":     "\u00DC",
  1662  	"Yacute":   "\u00DD",
  1663  	"THORN":    "\u00DE",
  1664  	"szlig":    "\u00DF",
  1665  	"agrave":   "\u00E0",
  1666  	"aacute":   "\u00E1",
  1667  	"acirc":    "\u00E2",
  1668  	"atilde":   "\u00E3",
  1669  	"auml":     "\u00E4",
  1670  	"aring":    "\u00E5",
  1671  	"aelig":    "\u00E6",
  1672  	"ccedil":   "\u00E7",
  1673  	"egrave":   "\u00E8",
  1674  	"eacute":   "\u00E9",
  1675  	"ecirc":    "\u00EA",
  1676  	"euml":     "\u00EB",
  1677  	"igrave":   "\u00EC",
  1678  	"iacute":   "\u00ED",
  1679  	"icirc":    "\u00EE",
  1680  	"iuml":     "\u00EF",
  1681  	"eth":      "\u00F0",
  1682  	"ntilde":   "\u00F1",
  1683  	"ograve":   "\u00F2",
  1684  	"oacute":   "\u00F3",
  1685  	"ocirc":    "\u00F4",
  1686  	"otilde":   "\u00F5",
  1687  	"ouml":     "\u00F6",
  1688  	"divide":   "\u00F7",
  1689  	"oslash":   "\u00F8",
  1690  	"ugrave":   "\u00F9",
  1691  	"uacute":   "\u00FA",
  1692  	"ucirc":    "\u00FB",
  1693  	"uuml":     "\u00FC",
  1694  	"yacute":   "\u00FD",
  1695  	"thorn":    "\u00FE",
  1696  	"yuml":     "\u00FF",
  1697  	"fnof":     "\u0192",
  1698  	"Alpha":    "\u0391",
  1699  	"Beta":     "\u0392",
  1700  	"Gamma":    "\u0393",
  1701  	"Delta":    "\u0394",
  1702  	"Epsilon":  "\u0395",
  1703  	"Zeta":     "\u0396",
  1704  	"Eta":      "\u0397",
  1705  	"Theta":    "\u0398",
  1706  	"Iota":     "\u0399",
  1707  	"Kappa":    "\u039A",
  1708  	"Lambda":   "\u039B",
  1709  	"Mu":       "\u039C",
  1710  	"Nu":       "\u039D",
  1711  	"Xi":       "\u039E",
  1712  	"Omicron":  "\u039F",
  1713  	"Pi":       "\u03A0",
  1714  	"Rho":      "\u03A1",
  1715  	"Sigma":    "\u03A3",
  1716  	"Tau":      "\u03A4",
  1717  	"Upsilon":  "\u03A5",
  1718  	"Phi":      "\u03A6",
  1719  	"Chi":      "\u03A7",
  1720  	"Psi":      "\u03A8",
  1721  	"Omega":    "\u03A9",
  1722  	"alpha":    "\u03B1",
  1723  	"beta":     "\u03B2",
  1724  	"gamma":    "\u03B3",
  1725  	"delta":    "\u03B4",
  1726  	"epsilon":  "\u03B5",
  1727  	"zeta":     "\u03B6",
  1728  	"eta":      "\u03B7",
  1729  	"theta":    "\u03B8",
  1730  	"iota":     "\u03B9",
  1731  	"kappa":    "\u03BA",
  1732  	"lambda":   "\u03BB",
  1733  	"mu":       "\u03BC",
  1734  	"nu":       "\u03BD",
  1735  	"xi":       "\u03BE",
  1736  	"omicron":  "\u03BF",
  1737  	"pi":       "\u03C0",
  1738  	"rho":      "\u03C1",
  1739  	"sigmaf":   "\u03C2",
  1740  	"sigma":    "\u03C3",
  1741  	"tau":      "\u03C4",
  1742  	"upsilon":  "\u03C5",
  1743  	"phi":      "\u03C6",
  1744  	"chi":      "\u03C7",
  1745  	"psi":      "\u03C8",
  1746  	"omega":    "\u03C9",
  1747  	"thetasym": "\u03D1",
  1748  	"upsih":    "\u03D2",
  1749  	"piv":      "\u03D6",
  1750  	"bull":     "\u2022",
  1751  	"hellip":   "\u2026",
  1752  	"prime":    "\u2032",
  1753  	"Prime":    "\u2033",
  1754  	"oline":    "\u203E",
  1755  	"frasl":    "\u2044",
  1756  	"weierp":   "\u2118",
  1757  	"image":    "\u2111",
  1758  	"real":     "\u211C",
  1759  	"trade":    "\u2122",
  1760  	"alefsym":  "\u2135",
  1761  	"larr":     "\u2190",
  1762  	"uarr":     "\u2191",
  1763  	"rarr":     "\u2192",
  1764  	"darr":     "\u2193",
  1765  	"harr":     "\u2194",
  1766  	"crarr":    "\u21B5",
  1767  	"lArr":     "\u21D0",
  1768  	"uArr":     "\u21D1",
  1769  	"rArr":     "\u21D2",
  1770  	"dArr":     "\u21D3",
  1771  	"hArr":     "\u21D4",
  1772  	"forall":   "\u2200",
  1773  	"part":     "\u2202",
  1774  	"exist":    "\u2203",
  1775  	"empty":    "\u2205",
  1776  	"nabla":    "\u2207",
  1777  	"isin":     "\u2208",
  1778  	"notin":    "\u2209",
  1779  	"ni":       "\u220B",
  1780  	"prod":     "\u220F",
  1781  	"sum":      "\u2211",
  1782  	"minus":    "\u2212",
  1783  	"lowast":   "\u2217",
  1784  	"radic":    "\u221A",
  1785  	"prop":     "\u221D",
  1786  	"infin":    "\u221E",
  1787  	"ang":      "\u2220",
  1788  	"and":      "\u2227",
  1789  	"or":       "\u2228",
  1790  	"cap":      "\u2229",
  1791  	"cup":      "\u222A",
  1792  	"int":      "\u222B",
  1793  	"there4":   "\u2234",
  1794  	"sim":      "\u223C",
  1795  	"cong":     "\u2245",
  1796  	"asymp":    "\u2248",
  1797  	"ne":       "\u2260",
  1798  	"equiv":    "\u2261",
  1799  	"le":       "\u2264",
  1800  	"ge":       "\u2265",
  1801  	"sub":      "\u2282",
  1802  	"sup":      "\u2283",
  1803  	"nsub":     "\u2284",
  1804  	"sube":     "\u2286",
  1805  	"supe":     "\u2287",
  1806  	"oplus":    "\u2295",
  1807  	"otimes":   "\u2297",
  1808  	"perp":     "\u22A5",
  1809  	"sdot":     "\u22C5",
  1810  	"lceil":    "\u2308",
  1811  	"rceil":    "\u2309",
  1812  	"lfloor":   "\u230A",
  1813  	"rfloor":   "\u230B",
  1814  	"lang":     "\u2329",
  1815  	"rang":     "\u232A",
  1816  	"loz":      "\u25CA",
  1817  	"spades":   "\u2660",
  1818  	"clubs":    "\u2663",
  1819  	"hearts":   "\u2665",
  1820  	"diams":    "\u2666",
  1821  	"quot":     "\u0022",
  1822  	"amp":      "\u0026",
  1823  	"lt":       "\u003C",
  1824  	"gt":       "\u003E",
  1825  	"OElig":    "\u0152",
  1826  	"oelig":    "\u0153",
  1827  	"Scaron":   "\u0160",
  1828  	"scaron":   "\u0161",
  1829  	"Yuml":     "\u0178",
  1830  	"circ":     "\u02C6",
  1831  	"tilde":    "\u02DC",
  1832  	"ensp":     "\u2002",
  1833  	"emsp":     "\u2003",
  1834  	"thinsp":   "\u2009",
  1835  	"zwnj":     "\u200C",
  1836  	"zwj":      "\u200D",
  1837  	"lrm":      "\u200E",
  1838  	"rlm":      "\u200F",
  1839  	"ndash":    "\u2013",
  1840  	"mdash":    "\u2014",
  1841  	"lsquo":    "\u2018",
  1842  	"rsquo":    "\u2019",
  1843  	"sbquo":    "\u201A",
  1844  	"ldquo":    "\u201C",
  1845  	"rdquo":    "\u201D",
  1846  	"bdquo":    "\u201E",
  1847  	"dagger":   "\u2020",
  1848  	"Dagger":   "\u2021",
  1849  	"permil":   "\u2030",
  1850  	"lsaquo":   "\u2039",
  1851  	"rsaquo":   "\u203A",
  1852  	"euro":     "\u20AC",
  1853  }
  1854  
  1855  // HTMLAutoClose is the set of HTML elements that
  1856  // should be considered to close automatically.
  1857  //
  1858  // See the Decoder.Strict and Decoder.Entity fields' documentation.
  1859  var HTMLAutoClose []string = htmlAutoClose
  1860  
  1861  var htmlAutoClose = []string{
  1862  	/*
  1863  		hget http://www.w3.org/TR/html4/loose.dtd |
  1864  		9 sed -n 's/<!ELEMENT ([^ ]*) +- O EMPTY.+/	"\1",/p' | tr A-Z a-z
  1865  	*/
  1866  	"basefont",
  1867  	"br",
  1868  	"area",
  1869  	"link",
  1870  	"img",
  1871  	"param",
  1872  	"hr",
  1873  	"input",
  1874  	"col",
  1875  	"frame",
  1876  	"isindex",
  1877  	"base",
  1878  	"meta",
  1879  }
  1880  
  1881  var (
  1882  	escQuot = []byte("&#34;") // shorter than "&quot;"
  1883  	escApos = []byte("&#39;") // shorter than "&apos;"
  1884  	escAmp  = []byte("&amp;")
  1885  	escLT   = []byte("&lt;")
  1886  	escGT   = []byte("&gt;")
  1887  	escTab  = []byte("&#x9;")
  1888  	escNL   = []byte("&#xA;")
  1889  	escCR   = []byte("&#xD;")
  1890  	escFFFD = []byte("\uFFFD") // Unicode replacement character
  1891  )
  1892  
  1893  // EscapeText writes to w the properly escaped XML equivalent
  1894  // of the plain text data s.
  1895  func EscapeText(w io.Writer, s []byte) error {
  1896  	return escapeText(w, s, true)
  1897  }
  1898  
  1899  // escapeText writes to w the properly escaped XML equivalent
  1900  // of the plain text data s. If escapeNewline is true, newline
  1901  // characters will be escaped.
  1902  func escapeText(w io.Writer, s []byte, escapeNewline bool) error {
  1903  	var esc []byte
  1904  	last := 0
  1905  	for i := 0; i < len(s); {
  1906  		r, width := utf8.DecodeRune(s[i:])
  1907  		i += width
  1908  		switch r {
  1909  		case '"':
  1910  			esc = escQuot
  1911  		case '\'':
  1912  			esc = escApos
  1913  		case '&':
  1914  			esc = escAmp
  1915  		case '<':
  1916  			esc = escLT
  1917  		case '>':
  1918  			esc = escGT
  1919  		case '\t':
  1920  			esc = escTab
  1921  		case '\n':
  1922  			if !escapeNewline {
  1923  				continue
  1924  			}
  1925  			esc = escNL
  1926  		case '\r':
  1927  			esc = escCR
  1928  		default:
  1929  			if !isInCharacterRange(r) || (r == 0xFFFD && width == 1) {
  1930  				esc = escFFFD
  1931  				break
  1932  			}
  1933  			continue
  1934  		}
  1935  		if _, err := w.Write(s[last : i-width]); err != nil {
  1936  			return err
  1937  		}
  1938  		if _, err := w.Write(esc); err != nil {
  1939  			return err
  1940  		}
  1941  		last = i
  1942  	}
  1943  	_, err := w.Write(s[last:])
  1944  	return err
  1945  }
  1946  
  1947  // EscapeString writes to p the properly escaped XML equivalent
  1948  // of the plain text data s.
  1949  func (p *printer) EscapeString(s string) {
  1950  	var esc []byte
  1951  	last := 0
  1952  	for i := 0; i < len(s); {
  1953  		r, width := utf8.DecodeRuneInString(s[i:])
  1954  		i += width
  1955  		switch r {
  1956  		case '"':
  1957  			esc = escQuot
  1958  		case '\'':
  1959  			esc = escApos
  1960  		case '&':
  1961  			esc = escAmp
  1962  		case '<':
  1963  			esc = escLT
  1964  		case '>':
  1965  			esc = escGT
  1966  		case '\t':
  1967  			esc = escTab
  1968  		case '\n':
  1969  			esc = escNL
  1970  		case '\r':
  1971  			esc = escCR
  1972  		default:
  1973  			if !isInCharacterRange(r) || (r == 0xFFFD && width == 1) {
  1974  				esc = escFFFD
  1975  				break
  1976  			}
  1977  			continue
  1978  		}
  1979  		p.WriteString(s[last : i-width])
  1980  		p.Write(esc)
  1981  		last = i
  1982  	}
  1983  	p.WriteString(s[last:])
  1984  }
  1985  
  1986  // Escape is like EscapeText but omits the error return value.
  1987  // It is provided for backwards compatibility with Go 1.0.
  1988  // Code targeting Go 1.1 or later should use EscapeText.
  1989  func Escape(w io.Writer, s []byte) {
  1990  	EscapeText(w, s)
  1991  }
  1992  
  1993  var (
  1994  	cdataStart  = []byte("<![CDATA[")
  1995  	cdataEnd    = []byte("]]>")
  1996  	cdataEscape = []byte("]]]]><![CDATA[>")
  1997  )
  1998  
  1999  // emitCDATA writes to w the CDATA-wrapped plain text data s.
  2000  // It escapes CDATA directives nested in s.
  2001  func emitCDATA(w io.Writer, s []byte) error {
  2002  	if len(s) == 0 {
  2003  		return nil
  2004  	}
  2005  	if _, err := w.Write(cdataStart); err != nil {
  2006  		return err
  2007  	}
  2008  	for {
  2009  		i := bytes.Index(s, cdataEnd)
  2010  		if i >= 0 && i+len(cdataEnd) <= len(s) {
  2011  			// Found a nested CDATA directive end.
  2012  			if _, err := w.Write(s[:i]); err != nil {
  2013  				return err
  2014  			}
  2015  			if _, err := w.Write(cdataEscape); err != nil {
  2016  				return err
  2017  			}
  2018  			i += len(cdataEnd)
  2019  		} else {
  2020  			if _, err := w.Write(s); err != nil {
  2021  				return err
  2022  			}
  2023  			break
  2024  		}
  2025  		s = s[i:]
  2026  	}
  2027  	_, err := w.Write(cdataEnd)
  2028  	return err
  2029  }
  2030  
  2031  // procInst parses the `param="..."` or `param='...'`
  2032  // value out of the provided string, returning "" if not found.
  2033  func procInst(param, s string) string {
  2034  	// TODO: this parsing is somewhat lame and not exact.
  2035  	// It works for all actual cases, though.
  2036  	param = param + "="
  2037  	idx := strings.Index(s, param)
  2038  	if idx == -1 {
  2039  		return ""
  2040  	}
  2041  	v := s[idx+len(param):]
  2042  	if v == "" {
  2043  		return ""
  2044  	}
  2045  	if v[0] != '\'' && v[0] != '"' {
  2046  		return ""
  2047  	}
  2048  	idx = strings.IndexRune(v[1:], rune(v[0]))
  2049  	if idx == -1 {
  2050  		return ""
  2051  	}
  2052  	return v[1 : idx+1]
  2053  }
  2054  

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