An @import atrule  @import "lib";  Depending on our environment, importing is done differently: In the browser, it's an XHR request, in Node, it would be a file-system operation. The function used for importing is stored in `import`, which we pass to the Import constructor.
function () {
                var path, features, index = parserInput.i;

                var dir = parserInput.$re(/^@import?\s+/);

                if (dir) {
                    var options = (dir ? this.importOptions() : null) || {};

                    if ((path = this.entities.quoted() || this.entities.url())) {
                        features = this.mediaFeatures();

                        if (!parserInput.$char(';')) {
                            parserInput.i = index;
                            error('missing semi-colon or unrecognised media features on import');
                        }
                        features = features && new(tree.Value)(features);
                        return new(tree.Import)(path, features, options, index, fileInfo);
                    }
                    else {
                        parserInput.i = index;
                        error('malformed import statement');
                    }
                }
            }