This mixes the attribute values, the indention labels and the numerical representation of the amount to indent all together.
* Can we call those 3 values (right, left, firstLine) `right_indent_pixels`, `left_indent_pixels` and I have no idea what `firstLine` is supposed to be/do, but it definitely shouldn't be camelCase.
* Can we create a `scale_foo_to_pixels` method for doing the math (I don't know what the starting unit is)?
* Can we stop coercing ints to strings here? It's kind of nutty. We could do eg: `right_indent_pixels = scale_foo_to_pixels(ind.attrib.get('right', 0))`

I'm cool with not trying to address the fundamental problem with setting classes on span elements here, but these seem like quick changes to clean this up.