A data-retrieval method for use on a portable electronic device. The method comprises receiving a query string at a user interface of the device and displaying one or more index strings on the user interface such that the relative prominence of each index string displayed increases with increasing resemblance of that index string to the query string. The method further comprises displaying an index string with greater prominence when a fixed-length substring of the query string occurs anywhere in the index string, regardless of position. In this manner, the relevance of prominently displayed index strings increases as more characters are appended to the query string, even if the query string contains errors.