5. The method of claim 1 , wherein identifying occurrences of the normalized data entries in the electronic resource comprises: identifying one or more tags in the electronic resource; parsing content text associated with each of the identified tags to determine whether the content text matches a normalized data entry; and marking an identified tag of the electronic resource with a navigation filter heading annotation in response to a determination that the content text associated with the identified tag matches one or more of the normalized data entries.
6. The method of claim 5 , further comprising, for each of the identified tags: determining whether the tag is a leaf node of the electronic resource; and removing the tag from consideration as a potential navigation filter heading in response to a determination that the tag is not a leaf.