XL 2013 petit problème dans une remontée récursive dans les instances de classe en poupée russe

Option Explicit
Public DocXML
Dim CustomUI As XmlElement, ribbon As XmlElement, tabs As XmlElement, XtaB As XmlElement, group As XmlElement, button As XmlElement
Sub test()
    Dim elem As XmlElement
    Set DocXML = New XmlElement


    Set CustomUI = DocXML.createElement("customUI")
    DocXML.AppendChild CustomUI

    Set ribbon = DocXML.createElement("ribbon")
    CustomUI.AppendChild ribbon
    Set tabs = DocXML.createElement("tabs")
    ribbon.AppendChild tabs

    Set XtaB = DocXML.createElement("tab")
'    XtaB.ID = "tab_" & tabs.childcount + 1
'    XtaB.label = "mon onglet"
    tabs.AppendChild XtaB, "tab_" & tabs.childcount + 1, "mon onglet"
    


    Set group = DocXML.createElement("group")
'    group.ID = "group_" & XtaB.childcount + 1
'    group.label = "mon onglet"
    XtaB.AppendChild group, "group_" & XtaB.childcount + 1, "mon onglet"


    Set button = DocXML.createElement("group")
'    button.ID = "button_" & group.childcount + 1
'    button.label = "mon bouton"
    group.AppendChild button, "button_" & group.childcount + 1, "mon bouton"

    Set button = DocXML.createElement("group")
'    button.ID = "button_" & group.childcount + 1
'    button.label = "mon bouton 2"
    group.AppendChild button, "button_" & group.childcount + 1, "mon bouton 2"


    Set elem = group.ChildNodes(1)
    MsgBox elem.ID
    MsgBox elem.parentX.ID

Dim D As XmlElement
   Set D = DocXML.getElementById(Cherche:="tab_1")
     MsgBox D.ID
    MsgBox D.parentX.ID
End Sub

Option Explicit
Public tagName As String
Public ID As String
Public label As String
Public childs As Collection, trouve As XmlElement
Public childcount As Long
Public parentX
Private Sub Class_Initialize()
  Set childs = New Collection
 End Sub

Public Function createElement(tagName) As XmlElement
    Set createElement = New XmlElement
    createElement.tagName = tagName
End Function

Public Function AppendChild(E As XmlElement, Optional ID As String = "", Optional label As String = "")
     childs.Add E
     Set childs(childs.Count).parentX = Me
     childcount = childs.Count
     childs(childcount).ID = ID
    childs(childcount).label = label
End Function

Public Function ChildNodes(Optional x As Long = -1) 'As XmlElement
    If x > -1 Then
        Set ChildNodes = childs(x)
    Else
        ChildNodes = childs
    End If
End Function

Public Function getElementById(Optional element As XmlElement = Nothing, Optional idx As String = "", Optional Cherche As String = "") As XmlElement
Dim i As Integer
   If element Is Nothing Then Set element = Me
  
   On Error Resume Next
    Debug.Print "|" & element.tagName
    If Cherche = element.ID Then Set trouve = element: Set parentX.trouve = element: Exit Function

    For i = 1 To element.childcount
        MsgBox element.childs(i).ID
       trouve = getElementById(element.childs(i), idx, Cherche)
       If Not (trouve Is Nothing) Then Set getElementById = trouve: Set parentX.trouve = element: Exit Function
    Next
    

 
End Function

Public Function AppendChild(ByVal e As XmlElement)
' avant d 'aller plus loin
'test de possibilité selon les règles de bases du xml schemas microsoft customUI
    Select Case e.tagName
    Case "button"
        If Not " group box menu buttonGroup dropDown " Like "* " & Me.tagName & " *" Then
            MsgBox " vous ne pouvez pas mette un " & e.tagName & " dans un " & Me.tagName: Set e = Nothing
            Exit Function
        End If
    Case "group"
        If Me.tagName <> "tab" Then MsgBox " vous ne pouvez pas mette un " & e.tagName & " dans un " & Me.tagName: Set e = Nothing: Exit Function

        'etc..etc..

    End Select


    Dim x&, z&
    x = UBound(childs) + 1
    ReDim Preserve childs(1 To x) As New XmlElement
    e.indent = Me.indent + 1
    Set childs(x) = e
    Set childs(x).parentX = Me
    childcount = x
    '******************************************************
    'l 'erreur se passe ici !!!
    'stockage des element dans la variable public allElements (mais celle de l'instance de docXML)
    ' MsgBox UBound(DocXML.AllElements)
    'z = UBound(DocXML.AllElements) + 1
    ' ReDim Preserve DocXML.AllElements(0 To z)
    'Set DocXML.AllElements(z) = e.id
    '******************************************************
End Function