{
Here I will show one way to parse XML document
The main concept of XML is using containers for XML objects -
so we will use Tree concept while building our XML object from XML document.
XML text uses containers (<TAG ... >...</TAG>) or simple definitions (<TAG ... />)
in each TAG we can use parameters (<TAG key1="value1" key2="value2">... <SIMPLE key3="value3"> ...</TAG>)
Finally we will have an array of objects, describing XML tags. Every object of this
class will have an array of children if needed, and a hash to describe properties of it.

For example if we have a text
<UL name="xxx">
 <LI name="xxx1"/>
 <LI name="xxx2"/>
 <LI name="xxx3"/>
 <LI name="xxx4"/>
</UL>
we will have one root object (named "UL") in wich we will have 4 children
(named "LI" with different sets of properties - from "NAME"="xxx1" to "NAME"="xxx4")
This is not a trivial task - so we will make a unit to solve this...
I will try to comment some here...
if you have any comments for this unit - write to me: sunworx@mail.ru; yz@infoteh.ru
}
unit YZXMLParser;
interface
uses
 SysUtils, ComCtrls;
type
 THashElement = record
  Key, Value: string;
 end;
type
 THashElementArr = array of THashElement;

 // here we declare a THash class to use in our parser
 // The concept of THash is to retreive named values from an array
 // Hash is an array where index is a string (example V[Key]=value,
 // whehe Key and Value are of type string)
 // The main purpose of this class is to rerurn a value of a String-named key
 //(example: s:=hash['someValue'])

 // the description of a hash element we use
type
 THash = class(TObject)
 private
  Arr: THashElementArr;
  function GetValue(Key: string): string;
  procedure SetValue(Key: string; const VValue: string);
  function GetKeys: StrArr;
  function GetValues: StrArr;
  function GetCount: Integer;
  function Getempty: Boolean;
 public
  property Value[Key: string]: string read GetValue write SetValue; default;
  property Values: StrArr read GetValues;
  property Keys: StrArr read GetKeys;
  property Count: Integer read GetCount;
  property Empty: Boolean read Getempty;
  procedure Clear;
  constructor Create;
  destructor Destroy; override;
 end;
 TYZHash = THash;

type
 // Here we declare some definitions for our parser to know what
 // identifier we would receive next in our text
 // these values will be used in the result of What() function which will scan text for keys
 TYZXMLMarker = (xmlOpenTag, xmlCloseTagShort, xmlCloseTag, xmlCloseTagLong,
  xmlEOF, xmlIdentifier, xmlunknown); / *
 Because we use recursive definition of our class(as TreeView, where we declare children of
  the same type in opur type
  declaration) we must use forward declaration
  * /

 // The definition of a TAG class

 TYZXMLTag = class;
 TYZXMLTags = array of TYZXMLTag;
 TYZXMLTag = class(TObject)
 private
  FData: TYZHash;
  FParent: TYZXMLTag;
  FName: string;
  function GetValue(AName: string): string;
  procedure SetName(const Value: string);
  procedure SetValue(AName: string; const Value: string);
  function GetCount: Integer;
  function GetValueNames: strarr;
 public
  Children: TYZXMLTags; // these are our child nodes
  Text: string;

  property Name: string read FName write SetName; // name of a tag
  property Values[AName: string]: string read GetValue write SetValue;
  default; // values of properties of a tag (hash values)
  property ValueNames: strarr read GetValueNames;
  // array of strings returniong names of all props of this tag
  property Count: Integer read GetCount;
  // a count of children of a tag (if this tag is a container)
  function SkipSpaces(var AData: string; var APos: Integer;
  RememberBreaks: Boolean = False): Char;
  // internal. for skip spaces (also CR or LF or other non-text chars) while parsing text
  function ParseValue(var AData: string; var APos: Integer): Boolean;
  // parse value (calling when found a parameter of a tag)
  function ParseName(var AData: string; var APos: Integer): Boolean;
  // parse key of parameter in a tag
  // these two procs used to parse any text found while parsing XML
  function ParseString(var AData: string; var APos: Integer;
  RememberBreaks: Boolean = False): string;
  function ParseQuotedString(var AData: string; var APos: Integer;
  QIndef: Char = '"'): string;
  // returnes the type of next identifier in XML
  function What(var AData: string; var APos: Integer;
  var A: Integer; RememberBreaks: Boolean = False): TYZXMLMarker;

  // This is a main procedure of our class - AData is a string,
  // containing all XML data (you can use TMemo.Text, for example, as a parameter of AData)
  function ParseXML(var AData: string; var APos: Integer): Boolean;
  // This function returnes a text string, built based on data, stored in an object.
  function GenerateXML(var AData: string; ATab: string = ''): Boolean;
  // returnes char from string at specified pos (#0 if not in range)
  function CharAt(var S: string; APos: Integer): Char;

  function TagNameExists(AName: string): Boolean;
  // Adds a child to children array of a current tag
  function AddChild: TYZXMLTag;
  // Initializes current tag and deletes all existing children
  procedure Clear; virtual;
  constructor Create(AParent: TYZXMLTag); virtual;
  destructor Destroy; virtual;
 end;

type
 TYZXMLParser = class(TYZXMLTag)
 private
  Header: TYZHash;
  procedure _BuildTreeView(ATreeView: TTreeView; ANode: TTreeNode; ATag: TYZXMLTag);
 public
  property HeaderValues: TYZHash read Header;
  procedure BuildTreeView(ATreeView: TTreeView);
  function Parse(AData: string): Boolean;
  function Generate(var AData: string): Boolean;
  constructor Create;
  destructor Destroy;
 end;
implementation
//==============================================================================
{ TYZXMLTag }
function TYZXMLTag.AddChild: TYZXMLTag;
begin
 setlength(children, Length(children) + 1);
 Result := TYZXMLTag.Create(Self);
 children[Length(children) - 1] := Result;
end;
//------------------------------------------------------------------------------
procedure TYZXMLTag.Clear;
var
 i: Integer;
begin
 for i := 0 to Count - 1 do if children[i] <> nil then Children[i].Destroy;
 setlength(children, 0);
 FData.Clear;
 Text := '';
end;
//------------------------------------------------------------------------------
constructor TYZXMLTag.Create(AParent: TYZXMLTag);
begin
 inherited Create;
 FData := TYZHash.Create;
 FParent := AParent;
 Clear;
end;
//------------------------------------------------------------------------------
destructor TYZXMLTag.Destroy;
begin
 Clear;
 FData.Destroy;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.GetCount: Integer;
begin
 Result := Length(children);
end;
//------------------------------------------------------------------------------
function TYZXMLTag.GetValue(AName: string): string;
begin
 Result := FData[AName];
end;
//------------------------------------------------------------------------------
function TYZXMLTag.ParseName(var AData: string; var APos: Integer): Boolean;
begin
 Result := False;
 FName := ParseString(AData, APos);
 if fname = '' then Exit;
 Result := True;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.ParseQuotedString(var AData: string; var APos: Integer;
 QIndef: Char = '"'): string;
var
 i: Integer;
 skipnext: Boolean;
 z: Char;
begin
 Result := '';
 if CharAt(AData, APos) <> QIndef then Exit;
 i := apos;
 skipnext := True;
 repeat
  if not skipnext then
  begin
  if charat(AData, I) = '\' then Skip := True
  else
  begin
  z := charat(AData, I);
  if (Z = QIndef) or (z = #0) then
  begin
  Result := Copy(AData, aPos + 1, I - APos - 1);
  // result:=exch(result,'\','');
  APos := I + 1;
  Exit;
  end;
  end;
  end
  else
  skipnext := False;
  Inc(i);
 until False;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.ParseString(var AData: string; var APos: Integer;
 RememberBreaks: Boolean = False): string;
const
 extsym: string = '=<>;?*/';
var
 nxt: Char;
 x1, x2, i: Integer;
begin
 Result := '';
 nxt := SkipSpaces(AData, APos, RememberBreaks);
 if nxt = #0 then Exit;
 if (nxt = '"') or (nxt = '''') then
 begin
  Result := ParseQuotedString(AData, APos);
  Exit;
 end;
 x1 := APos;
 i := x1;
 nxt := CharAt(AData, i);
 while ((Ord(nxt) <= 32) or (Pos(nxt, extsym) > 0)) and (nxt <> #0) do
 begin
  Inc(i);
  nxt := CharAt(AData, i);
 end;
 APos := i;
 X1 := APos;
 while (Ord(nxt) > 32) and (Pos(nxt, extsym) <= 0) do
 begin
  Inc(i);
  nxt := CharAt(AData, i);
 end;
 x2 := i - x1;
 Result := Copy(AData, x1, x2);
 APos := i;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.ParseValue(var AData: string; var APos: Integer): Boolean;
var
 n, v: string;
 i, x: Integer;
begin
 Result := False;
 n := parseString(AData, APos);
 if n = '' then Exit;
 if skipspaces(AData, APos) <> '=' then Exit;
 Inc(apos);
 V := parseString(AData, APos);
 fdata[n] := dequote(v);
 Result := True;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.ParseXML(var AData: string; var APos: Integer): Boolean;
var
 N: TYZXMLMarker;
 nxt: Integer;
 isLong: Boolean;
 inTag: Boolean;
begin
 isLong := False;
 Result := False;
 Clear;
 if What(AData, APos, nxt) <> xmlOpenTag then Exit;
 APos := nxt;
 if What(AData, APos, nxt) <> xmlIdentifier then Exit;
 Result := ParseName(AData, APos);
 if not Result then Exit;
 intag := True;
 Result := False;
 while True do
 begin
  N := What(AData, APos, nxt, (not intag and islong and (Count > 0)));
  case N of
  xmlEOF: Exit;
  xmlCloseTagLong:
  begin
  Result := True;
  if islong then APos := nxt;
  if (Text <> '') and (Count > 0) then
  begin
  Text := exch(Text, #13#10#13#10, #13#10);
  end;
  Exit;
  end;
  xmlCloseTagShort:
  begin
  Result := (not IsLong) and intag;
  if Result then APos := nxt;
  Exit;
  end;
  xmlOpenTag:
  begin
  if islong then Result := AddChild.ParseXML(AData, APos)
  else
  begin
  Result := False;
  Exit;
  end;
  if not Result then Exit;
  end;
  xmlCloseTag:
  begin
  IsLong := True;
  APos := nxt;
  intag := False;
  end;
  xmlIdentifier:
  begin
  if intag then parsevalue(AData, APos)
  else
  Text := Text + ParseString(AData, APos, True)
  end;
  xmlUnknown:
  begin
  Result := True;
  Exit;
  end;
  end;
 end;
end;
//------------------------------------------------------------------------------
procedure TYZXMLTag.SetName(const Value: string);
begin
 FName := Value;
end;
//------------------------------------------------------------------------------
procedure TYZXMLTag.SetValue(AName: string; const Value: string);
begin
 FData[AName] := Value;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.SkipSpaces(var AData: string; var APos: Integer;
 RememberBreaks: Boolean = False): Char;
var
 L: Integer;
 P: Char;
begin
 L := Length(AData);
 while APos <= L do
 begin
  P := AData[APos];
  if Ord(p) > 32 then
  begin
  Result := p;
  Exit;
  end
  else if rememberbreaks then
  begin
  if Pos(p, #13#9' ') > 0 then
  Text := Text + ' ';
  end;
  Inc(APos);
 end;
 Result := #0;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.CharAt(var S: string; APos: Integer): Char;
begin
 Result := #0;
 if (Length(s) < APos) or (apos < 1) then Exit;
 Result := s[APos];
end;
//------------------------------------------------------------------------------
function TYZXMLTag.What(var AData: string; var APos: Integer;
 var A: Integer; RememberBreaks: Boolean = False): TYZXMLMarker;
var
 s: string;
 C: Char;
 P: Integer;
begin
 Result := xmlEOF;
 P := APos;
 C := SkipSpaces(AData, APos);
 P := APos;
 A := P;
 if C = #0 then Exit;
 if C = '<' then if CharAt(AData, P + 1) = '/' then
  begin
  Inc(P, 2);
  s := parsestring(AData, P);
  if (uppercase(s) = uppercase(FName)) and (SkipSpaces(AData, P) = '>') then
  begin
  A := P + 1;
  Result := xmlCloseTagLong;
  Exit;
  end
  else
  begin
  if TagNameExists(s) then
  begin
  Result := xmlCloseTagLong;
  A := APos;
  Exit;
  end;
  A := P + 1;
  Result := xmlCloseTagLong;
  Exit;
  end;
  end;
 if C = '<' then
 begin
  A := P + 1;
  Result := xmlOpenTag;
  Exit;
 end;
 if C = '>' then
 begin
  A := P + 1;
  Result := xmlCloseTag;
  Exit;
 end;
 if C = '/' then if CharAt(AData, P + 1) = '>' then
  begin
  A := P + 2;
  Result := xmlCloseTagShort;
  Exit;
  end;
 A := P;
 parsestring(AData, A);
 Result := xmlIdentifier;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.GetValueNames: strarr;
begin
 Result := FData.Keys;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.GenerateXML(var AData: string; ATab: string = ''): Boolean;
var
 valDelimiter: string;
 spc: string;
 i: Integer;
 a: strarr;
begin
 spc := ATab + #9;
 if FData.Count < 5 then valDelimiter := ' '
 else
  valDelimiter := #13#10 + spc;
 AData := AData + #13#10 + ATab + '<' + FName;
 a := FData.keys;
 for i := 0 to Length(a) - 1 do
 begin
  AData := AData + valDelimiter + a[i] + ' = "' + EnQuote(values[a[i]]) + '"';
 end;
 if (Count > 0) or (Text <> '') then
 begin
  AData := AData + '>' + Text;
  for i := 0 to Count - 1 do
  begin
  Children[i].GenerateXML(AData, ATab + #9);
  end;
  AData := AData + #13#10 + ATab + '</' + FName + '>';
 end
 else
  AData := AData + '/>';
 Result := True;
end;
//------------------------------------------------------------------------------
function TYZXMLTag.TagNameExists(AName: string): Boolean;
begin
 Result := AnsiUpperCase(AName) = AnsiUpperCase(Self.FName);
 if Self.FParent = nil then Exit;
 if not Result then Result := fparent.TagNameExists(AName);
end;
//==============================================================================

{ TYZXMLParser }
constructor TYZXMLParser.Create;
begin
 Header := TYZHash.Create;
 inherited Create(nil);
end;
//------------------------------------------------------------------------------
destructor TYZXMLParser.Destroy;
begin
 inherited;
 Header.Destroy;
end;
//------------------------------------------------------------------------------
procedure TYZXMLParser.BuildTreeView(ATreeView: TTreeView);
var
 i: Integer;
begin
 // clear;
 ATreeView.Items.Clear;
 for i := 0 to Count - 1 do _BuildTreeView(ATreeView, nil, children[i]);
end;
//------------------------------------------------------------------------------
procedure TYZXMLParser._BuildTreeView(ATreeView: TTreeView; ANode: TTreeNode;
 ATag: TYZXMLTag);
var
 i: Integer;
 N: TTreeNode;
begin
 N := ATreeView.Items.AddChildObject(ANode, ATag.Name + ' ' + FData['ID'], Pointer(ATag));
 for i := 0 to ATag.Count - 1 do
 begin
  if ATag.children[i] <> nil then _BuildTreeView(ATreeView, N, ATag.children[i])
  else
  ATreeView.Items.AddChild(N, 'nil');
 end;
 N.Expanded := True;
end;
//------------------------------------------------------------------------------
function TYZXMLParser.Parse(AData: string): Boolean;
var
 x1, x2, X, i: Integer;
 s: string;
 tmp: TYZXMLTag;
 a: strarr;
 N: TYZXMLMarker;
begin
 X := 1;
 Self.SkipSpaces(AData, X);
 x2 := -1;
 Result := False;
 Clear;
 Header.Clear;
 x1 := Pos('<?', AData);
 if x1 >= X then
 begin
  x2 := Pos('?>', AData);
  if x2 < X then Exit;
  s := uppercase(Copy(AData, x1 + 2, 4));
  if Pos('XML ', s) <> 1 then Exit;
  s := '<xml ' + Copy(AData, x1 + 6, x2 - x1 - 6) + '/>';
  tmp := TYZXMLTag.Create(nil);
  tmp.ParseXML(s, x);
  a := tmp.ValueNames;
  for i := 0 to Length(a) - 1 do
  Header[a[i]] := tmp.Values[a[i]];
  tmp.Destroy;
  x := x2 + 2;
 end;
 Result := True;
 repeat
  N := whatnext(AData, X, x1);
  case N of
  xmlOpenTag: Result := Result and AddChild.ParseXML(AData, X);
  xmlIdentifier:
  begin
  if Text <> '' then Text := Text + ' ';
  Text := Text + parsestring(AData, X, True);
  end;
  else
  Parsestring(AData, X);
  end;
 until skipspaces(adata, x) = #0;
 // if not result then ShowMessage('Error Parsing: '+inttostr(X));
end;

function TYZXMLParser.Generate(var AData: string): Boolean;
var
 i: Integer;
 a: strarr;
begin
 Header['Date'] := DateTimeToStr(now);
 a := header.Keys;
 AData := '<?xml';
 for i := 0 to Length(a) - 1 do
  AData := AData + ' ' + a[i] + '="' + Header[a[i]] + '"';
 AData := AData + '?>'#13#10 + Text;
 Result := True;
 for i := 0 to Length(children) - 1 do
 begin
  Result := Result and children[i].generatexml(AData);
 end;
end;
//==============================================================================

// procedures of THash class

//==============================================================================
{THASH CLASS}

procedure THash.Clear;
begin
 SetLength(Arr, 0);
end;
constructor THash.Create;
begin
 inherited;
 Clear;
end;
//------------------------------------------------------------------------------
destructor THash.Destroy;
begin
 Clear;
 inherited;
end;
//------------------------------------------------------------------------------
function THash.GetCount: Integer;
begin
 Result := Length(Arr);
end;
//------------------------------------------------------------------------------
function THash.Getempty: Boolean;
begin
 Result := Length(Arr) = 0;
end;
function THash.GetKeys: StrArr;
var
 i: Integer;
begin
 SetLength(Result, Length(arr));
 for i := 0 to Length(Result) - 1 do
  Result[i] := arr[i].Key;
end;
//------------------------------------------------------------------------------
function THash.GetValue(Key: string): string;
var
 i: Integer;
 r: Boolean;
begin
 Result := '';
 i := 0;
 r := False;
 while (i < Length(Arr)) and (not r) do
 begin
  if AnsiUpperCase(arr[i].key) = AnsiUpperCase(Key) then
  begin
  Result := Arr[i].Value;
  r := True;
  end;
  i := i + 1;
 end;
end;
//------------------------------------------------------------------------------
function THash.GetValues: StrArr;
var
 i: Integer;
begin
 SetLength(Result, Length(arr));
 for i := 0 to Length(Result) - 1 do
  Result[i] := arr[i].Value;
end;
//------------------------------------------------------------------------------
procedure THash.SetValue(Key: string; const VValue: string);
var
 i, j: Integer;
 r: Boolean;
 E: THashElementArr;
begin
 if VValue <> '' then
 begin
  i := 0;
  r := False;
  while (i < Length(Arr)) and not r do
  begin
  if AnsiUpperCase(arr[i].key) = AnsiUpperCase(Key) then
  begin
  Arr[i].Value := VValue;
  r := True;
  end;
  i := i + 1;
  end;
  if not r then
  begin
  SetLength(Arr, Length(arr) + 1);
  arr[Length(arr) - 1].Key := Key;
  arr[Length(arr) - 1].Value := Vvalue;
  end;
 end;
 SetLength(E, Length(Arr));
 for i := 0 to Length(arr) - 1 do E[i] := Arr[i];
 SetLength(arr, 0);
 for i := 0 to Length(E) - 1 do if (E[i].Key <> '') and (E[i].Value <> '') then
  begin
  j := Length(arr);
  setlength(arr, j + 1);
  arr[j] := E[i];
  end;
end;
end.