function FoldLine(foldData, folds) {
    this.foldData = foldData;
    if (Array.isArray(folds)) {
        this.folds = folds;
    } else {
        folds = this.folds = [ folds ];
    }

    var last = folds[folds.length - 1]
    this.range = new Range(folds[0].start.row, folds[0].start.column,
                           last.end.row, last.end.column);
    this.start = this.range.start;
    this.end   = this.range.end;

    this.folds.forEach(function(fold) {
        fold.setFoldLine(this);
    }, this);
}
If an array is passed in, the folds are expected to be sorted already.