nl_tokens: https : // dom . spec . whatwg . org / #find - a - slot
pl_tokens: function findSlot ( slotable , openFlag ) { const { parentNode : parent } = slotable ; if ( ! parent ) { return null ; } const shadow = parent . _shadowRoot ; if ( ! shadow || ( openFlag && shadow . <mask> !== "open" ) ) { return null ; } for ( const child of domSymbolTree . treeIterator ( shadow ) ) { if ( isSlot ( child ) && child . name === slotable . _slotableName ) { return child ; } } return null ; }