Running cargo doc to test this out gives the following error:

warning: unresolved link to `reactive_graph::owner::Owner::on_cleanup`
  --> tachys/src/html/element/element_ext.rs:49:37
   |
49 |     /// Consider using [on_cleanup](reactive_graph::owner::Owner::on_cleanup) to delay dropping:
   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no item named `reactive_graph` in scope
   |
   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

and a broken link.

This is because the reactive_graph crate is not necessarily included but is an opt-in feature. Perhaps some text similar to the must_use message, or maybe just mentioning "If you're using this with Leptos, you can use on_cleanup"? I never know exactly how to handle these situations where the crate is designed for more general purpose use but there are Leptos-specific docs that would be useful.