Browsers also let you save documents, and perform a variety of other helpful tasks. Every day information providers add new Web servers to the net. There is no central clearing house or official registration cite for these servers. A few locations on the Web specialize in indexing Web pages. The search usually includes a document's Title, Main header, first few text lines, and sometimes author or server location information.
Some sites do a more thorough search than others resulting in a more useful database.
Given the dynamic nature of the Web and its vast size, the frequency that the database is re-indexed is critical to how useful the site will be. Good sites are very busy. Since this may or may not happen subject lists provide only a tiny fraction of the possible sources related to any given topic. Nevertheless, they are excellent starting points. Some examples are Yahoo , Galaxy , the Whole Internet Catalog , and the Clearinghouse for subject-Oriented Internet Resources .