I am running on `WP 4.7.2` and `Yoast SEO 4.4`.
I want to append a PHP variable to all titles. But it seems I am not able to do that. 

I have read that `wp_title` used to be the method before WP 4.4, then it was removed, and then it was returned because of some 'bug'?

I have tried using the `wpseo`+`add_filter` method, but it does not set the site title. 

I have searched `/wp-content/plugins/wordpress-seo` via `grep -r '<title>' *` and am not seeing where the plugin sets the title tag. It did return few lines, but none of them seem to be related. 

I found the following code in `clss-frontend.php`:

```
// When using WP 4.4, just use the new hook.
add_filter( 'pre_get_document_title', array( $this, 'title' ), 15 );
add_filter( 'wp_title', array( $this, 'title' ), 15, 3 );

```