code: def _update_document_tree(
              self,
              oldContent=None,
              newContent=None):
          
          self.refresh
          if self.parent:
              self.refresh
              indentOldContent = ""
              indentNewContent = ""
              for l in oldContent.split("\n"):
                  indentOldContent += "\t" + l + "\n"
              uoldContent = indentOldContent[:-1]
              for l in newContent.split("\n"):
                  indentNewContent += "\t" + l + "\n"
              unewContent = indentNewContent[:-1]
  
              thisOldContent = self.to_string(indentLevel=1)
              thisNewContent = thisOldContent.replace(uoldContent, unewContent)
  
              self.content = self.to_string(
                  indentLevel=0, title=False).replace(oldContent, newContent)
  
              self.content = self.to_string(
                  indentLevel=0, title=False).replace(oldContent, newContent)
  
              # REPLACE THE NEW CONTENT OF THIS PROJECT IN THE PARENT OBJECT'S
              # CONTENT
              doc = self.parent._update_document_tree(
                  oldContent=thisOldContent,
                  newContent=thisNewContent
              )
  
          else:
              self.content = self.content.replace(oldContent, newContent)
              doc = self
  
          self.refresh
          return doc
docs: *update document tree*
  
          **Key Arguments:**
              - ``oldContent`` -- the old content to be replaced in parent object (user sould not need to give this)
              - ``newContent`` -- the replacement text for the parent object  (user sould not need to give this)
  
          **Return:**
              - ``doc`` -- the updated document object