The find a range from a node list steps, which is the place in the spec where the actual string search is performed, uses the CharacterData of each node.

CharacterData is the raw data provided in the markup, e.g.:

<div>hello          world</div>

Will include all 10 spaces in CharacterData, even though they're collapsed into a single space when rendered.

The spec needs to specify exactly how we perform this collapsing.