If someone turns something into a heading that is before a start node, it should not number that heading. This is part of the behavior I was trying to implement so that the user can choose which parts of the document have heading numbering. In the future, I was planning on letting the user select which headings have the start node class, allowing them to control which portions of the document have heading numbering.

Looking over what I have now again, I realize it doesn't make much sense now. I reimplemented this so that it automatically makes the first heading in the document a start node so that it always applies heading numbering to the whole document for the time being until I further implement the ability for the user to choose which headings are start nodes in another ticket.

The line `parseInt($startNode[0].nodeName.slice(-1), 10)` is what I use to get the integer level of the heading. For example, if `$startNode` is an `h2` heading, this line will give me the integer `2`. Is there a better way to do this?