The Stack.attr() method adds an attribute to the stack and returns the original stack. Setting the third parameter to true will replace the value of the attribute instead of adding it.

Stack.attr() signature

Stack stack.attr(
  string name,
  mixed value,
  bool overwrite = false

If the third parameter is set to true it will call this.attributes.set() instead, thereby overwriting the value of the attribute.

This method is chainable as it returns the Stack object