Object Deletion in Sequence Diagrams

[WeiJie96]

May I ask when we should the object deletion symbol in sequence diagrams, in particular for AB3?

For delete command, only the parser gets deleted, but not the command itself.

Whereas for undo command, the command gets deleted.

[damithc]

It's an optional thing. You can use it wherever you think the object deletion is important enough to be specifically shown to the reader. Showing it makes the diagram more informative while omitting it doesn't make the diagram wrong.
In this example, I think it's an oversight. Both objects get deleted and X can be used for both.

[WeiJie96]

Thank you, Prof!