<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def open( self, **kwargs ):
 """Append an opening tag."""


        if self.tag in self.parent.twotags or self.tag in self.parent.onetags:
            self.render( self.tag, False, None, kwargs )
        elif self.mode == 'strict_html' and self.tag in self.parent.deptags:
            raise DeprecationError( self.tag )