code: def push(self, style={}):
          
          _style = {}
          for attr in style:
              if attr in self.cmds and not style[attr] in self.cmds[attr]:
                  print 'WARNING: ESC/POS PRINTING: ignoring invalid value: '+utfstr(style[attr])+' for style: '+utfstr(attr)
              else:
                  _style[attr] = self.enforce_type(attr, style[attr])
          self.stack.append(_style)
docs: push a new level on the stack with a style dictionnary containing style:value pairs