docs: def _init_formats(self):
          """
          Initialise default formats.
          """
          theme = self._color_scheme
          # normal message format
          fmt = QtGui.QTextCharFormat()
          fmt.setForeground(theme.foreground)
          fmt.setBackground(theme.background)
          self._formats[OutputFormat.NormalMessageFormat] = fmt
  
          # error message
          fmt = QtGui.QTextCharFormat()
          fmt.setForeground(theme.error)
          fmt.setBackground(theme.background)
          self._formats[OutputFormat.ErrorMessageFormat] = fmt
  
          # debug message
          fmt = QtGui.QTextCharFormat()
          fmt.setForeground(theme.custom)
          fmt.setBackground(theme.background)
          self._formats[OutputFormat.CustomFormat] = fmt