pub fn subsequent_load_determinant_fn(
        &mut self,
        val: impl Fn(&ClientError) -> bool + Send + Sync + 'static,
    ) -> &mut Self {
        self.subsequent_load_determinant = Box::new(val);
        self
    }
Sets the function that determines if an error on a *subsequent load*
should be presented to the user as taking up the whole page, or just
being in a little popup. Usually, you can leave this as the default,
which will display any internal errors as popups, and any errors from
the server (e.g. a 404 not found) as full pages.

You could use this to create extremely unorthodox patterns like
rendering a popup on the current page if the user clicks a link that
goes to a 404, if you really wanted.

For widgets, returning `true` from the function you provide to this will
take up the whole widget, as opposed to the whole page.

*Note: if you want all your errors to take up the whole page no matter
what (not recommended, see the book for why!), you should leave this
function as the default and simply style `#__perseus_error_popup` to
take up the whole page.*
packages/perseus/src/error_views.rs