src/sap.ui.core/src/sap/ui/thirdparty/less.js
function(isRule) {
                var elements, e, index = i, option, extendList, extend;

                if (!(isRule ? $re(/^&:extend\(/) : $re(/^:extend\(/))) { return; }

                do {
                    option = null;
                    elements = null;
                    while (! (option = $re(/^(all)(?=\s*(\)|,))/))) {
                        e = this.element();
                        if (!e) { break; }
                        if (elements) { elements.push(e); } else { elements = [ e ]; }
                    }

                    option = option && option[1];

                    extend = new(tree.Extend)(new(tree.Selector)(elements), option, index);
                    if (extendList) { extendList.push(extend); } else { extendList = [ extend ]; }

                } while($char(","));

                expect(/^\)/);

                if (isRule) {
                    expect(/^;/);
                }

                return extendList;
            }
function(isRule) {
                var elements, e, index = i, option, extendList, extend;

                if (!(isRule ? $re(/^&:extend\(/) : $re(/^:extend\(/))) { return; }

                do {
                    option = null;
                    elements = null;
                    while (! (option = $re(/^(all)(?=\s*(\)|,))/))) {
                        e = this.element();
                        if (!e) { break; }
                        if (elements) { elements.push(e); } else { elements = [ e ]; }
                    }

                    option = option && option[1];

                    extend = new(tree.Extend)(new(tree.Selector)(elements), option, index);
                    if (extendList) { extendList.push(extend); } else { extendList = [ extend ]; }

                } while($char(","));

                expect(/^\)/);

                if (isRule) {
                    expect(/^;/);
                }

                return extendList;
            }
function ( isRule ) { var elements , e , index = i , option , extendList , extend ; if ( ! ( isRule ? $re ( / ^&:extend\( / ) : $re ( / ^:extend\( / ) ) ) { return ; } do { option = null ; elements = null ; while ( ! ( option = $re ( / ^(all)(?=\s*(\)|,)) / ) ) ) { e = this . element ( ) ; if ( ! e ) { break ; } if ( elements ) { elements . push ( e ) ; } else { elements = [ e ] ; } } option = option && option [ 1 ] ; extend = new ( tree . Extend ) ( new ( tree . Selector ) ( elements ) , option , index ) ; if ( extendList ) { extendList . push ( extend ) ; } else { extendList = [ extend ] ; } } while ( $char ( "," ) ) ; expect ( / ^\) / ) ; if ( isRule ) { expect ( / ^; / ) ; } return extendList ; }
extend syntax - used to extend selectors
extend syntax - used to extend selectors