In order to have a better understanding of what Drupal does, I need to find out what the order of execution of hooks and page components is.
A page layout in Drupal consists of HTML, regions, nodes, blocks, Views and ... . Every one of these components have lots of preprocess or process functions, like
hook_preprocess_node. There are also template functions, theme functions and ... that are run to build the page array.
To avoid my question to be too broad, let's only talk about the hook and preprocess functions not the core functions.