This is not efficient. And it's not correct unless the Selector happens to start on the same line as ```point```.
Use the snapshot of ```point``` to find the containing line of ```item.Start```. Then the column is just ```item.Start - containingLine.Start```.
I always avoid getting the text of stylesheet tree items if possible because it requires allocating new memory. The snapshot already knows where all the line breaks are, so take advantage of that.