How is focus set on title in editview?

I’m making a button that creates a new editmode tiddler but I want the focus to be set on the title, just like when clicking TWs native New tiddler button. I’m guessing I should use tm-focus-selector but what’s the $param? (btw, the linked doc says there is no $ prefix on param but the core code does seem to use it)

<$button> new
<$action-sendmessage $message="tm-new-tiddler" tags="foo" />
<$action-sendmessage $message="tm-focus-selector" $param="????????" />
</$button>

Various core code tiddlers imply that $param should be some css class (e.g tc-titlebar tc-edit-texteditor - which doesn’t work) but the values used in the core are constructed in some cryptic ways…

Thanx!