Drupal 7 understanding theme registry

Theme registry is built and cached by the drupal core as part of booting process. The function "_theme_build_registry" (theme.inc) builds the theme registry. Each and every implemented theming hook will have a corresponding entry inside the theme registry. Basically each entry indicates  the process that takes place on invoking  the theming hook to which the entry belongs.  For the default bartik theme an entry inside theme registry for the theme hook "menu_link" looks like some thing as shown bellow.