code: def add_feature(self,var):
          
          if self.has_feature(var):
              return
          n=self.xmlnode.newChild(None, "feature", None)
          n.setProp("var", to_utf8(var))
docs: Add a feature to `self`.
  
          :Parameters:
              - `var`: the feature name.
          :Types:
              - `var`: `unicode`