def set_attr(name, value)
      if value.nil?
        new_attrs = {}
        attributes.each do |nam,val|
          new_attrs[nam] = val unless nam == name.to_s
        end
      else
        new_attrs = attributes.merge(name.to_s => value.to_s)
      end
      self.class.new(self.tag, new_attrs, self.children)
    end
def set_attr(name, value)
      if value.nil?
        new_attrs = {}
        attributes.each do |nam,val|
          new_attrs[nam] = val unless nam == name.to_s
        end
      else
        new_attrs = attributes.merge(name.to_s => value.to_s)
      end
      self.class.new(self.tag, new_attrs, self.children)
    end
Set an attribute, used internally by #attr

 Setting an attribute to nil will delete it

 @param name [String|Symbol]
 @param value [String|NilClass]
 @return [Hexp::Node]

 @api private