lib/less/parser/parser.js
function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (curly = parserInput.$re(/^\$\{([\w-]+)\}/))) {
                        return new(tree.Property)('$' + curly[1], index, fileInfo);
                    }
                }
function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (curly = parserInput.$re(/^\$\{([\w-]+)\}/))) {
                        return new(tree.Property)('$' + curly[1], index, fileInfo);
                    }
                }
function ( ) { var curly , index = parserInput . i ; if ( parserInput . currentChar ( ) === '$' && ( curly = parserInput . $re ( / ^\$\{([\w-]+)\} / ) ) ) { return new ( tree . Property ) ( '$' + curly [ 1 ] , index , fileInfo ) ; } }
A property entity useing the protective {} e.g. ${prop}
A property entity useing the protective {} e . g . $ { prop }