Search module of Drupal is a decent effort to optimize database searching, Salient features of drupal search are CJK handling, incremental revision index update among many others. Search in drupal is not one massive component which takes care of overall site search, it rather provides a framework based on hooks (drupal way of doing things) for other modules to interact with indexing,searching process; Though its search module which does actual parsing and all nitty gritty of regular expressions.
Hooks Exposed by Search Module
There are three major hooks exposed by search module:
