It is used in information filtering, information retrieval, indexing and relevancy rankings. Search engines have become popular tools for indexing and searching through such data, especially text. Indexers add array-like indexing capabilities to objects. It uses a dot syntax for indexing arrays and dictionaries. This complements basic techniques such as dictionary coding, Huffman coding and color indexing transform. Wikipedia gained early contributors from Nupedia, Slashdot postings, and web search engine indexing. This practice is also known as collaborative tagging, social classification, social indexing, and social tagging. Hence the format is convenient for automatic processing, indexing, and ebook collection management. Data processing begins with "indexing" the reflections. Computerized indexing and searching is also available. An example of a controlled vocabulary which is usable for indexing web pages is PSH. Searches can be based on full-text or other content-based indexing. The first automated citation indexing was done by CiteSeer in 1997. Today, a variety of indexing algorithms have been presented. Objects contain additional descriptive properties which can be used for better indexing or management.