1. A computer-implemented method, comprising: segmenting textual content for each of a plurality of distinct content items into word strings, each word string including a predefined number of contiguous words in the textual content of a content item; classifying word strings having a frequency of occurrence that is less than a threshold frequency of occurrence as uncommon word strings, the frequency of occurrence for each word string being a number of occurrences of the word string in the plurality of distinct content items relative to a total number of word strings in the plurality of distinct content items; identifying matching uncommon word strings between pairs of distinct content items; and determining a rank score for each distinct content item based on the matching uncommon word strings, the rank score being a score indicative of the importance of each distinct content item relative to other distinct content items.