old_contents: # encoding: utf-8
  
  """
  Custom element classes related to the styles part
  """
  
  from ..xmlchemy import BaseOxmlElement, ZeroOrMore, ZeroOrOne
  
  
  class CT_Style(BaseOxmlElement):
      """
      A ``<w:style>`` element, representing a style definition
      """
      pPr = ZeroOrOne('w:pPr', successors=(
          'w:rPr', 'w:tblPr', 'w:trPr', 'w:tcPr', 'w:tblStylePr'
      ))
  
  
  class CT_Styles(BaseOxmlElement):
      """
      ``<w:styles>`` element, the root element of a styles part, i.e.
      styles.xml
      """
      style = ZeroOrMore('w:style', successors=())
  
      def style_having_styleId(self, styleId):
          """
          Return the ``<w:style>`` child element having ``styleId`` attribute
          matching *styleId*.
          """
          xpath = './w:style[@w:styleId="%s"]' % styleId
          try:
              return self.xpath(xpath)[0]
          except IndexError:
              raise KeyError('no <w:style> element with styleId %d' % styleId)
  
new_contents: # encoding: utf-8
  
  """
  Custom element classes related to the styles part
  """
  
  from ..xmlchemy import BaseOxmlElement, ZeroOrMore, ZeroOrOne
  
  
  class CT_Style(BaseOxmlElement):
      """
      A ``<w:style>`` element, representing a style definition
      """
      pPr = ZeroOrOne('w:pPr', successors=(
          'w:rPr', 'w:tblPr', 'w:trPr', 'w:tcPr', 'w:tblStylePr'
      ))
  
  
  class CT_Styles(BaseOxmlElement):
      """
      ``<w:styles>`` element, the root element of a styles part, i.e.
      styles.xml
      """
      style = ZeroOrMore('w:style', successors=())
  
      def style_having_styleId(self, styleId):
          """
          Return the ``<w:style>`` child element having ``styleId`` attribute
          matching *styleId*.
          """
          xpath = './w:style[@w:styleId="%s"]' % styleId
          try:
              return self.xpath(xpath)[0]
          except IndexError:
              raise KeyError('no <w:style> element with styleId %s' % styleId)
  
subject: correct error message template