Vector first reverses the order of horizontal nav elements in HTML and then prevents flipping of float:left rules in CSS to make the interface looks the same in LTR and RTL environments.
Similar craziness is done to the search form - the input and the button are rendered in different order in LTR and RTL.
This causes T36587 and led to issues like T57779 in the past.
// Reverse horizontally rendered navigation elements if ( $this->data['rtl'] ) { $this->data['view_urls'] = array_reverse( $this->data['view_urls'] ); $this->data['namespace_urls'] = array_reverse( $this->data['namespace_urls'] ); $this->data['personal_urls'] = array_reverse( $this->data['personal_urls'] ); } ... // If there's a series of elements, reverse them when in RTL mode } elseif ( $this->data['rtl'] ) { $elements = array_reverse( $elements ); } ... etc
div.vectorTabs { /* @noflip */ float: left; ... ul { /* @noflip */ float: left; ... li { /* @noflip */ float: left; ... etc
Why would anyone do that is just mind-boggling to me. I assume it's a workaround for some IE6 bugs.