Editing/modifying drupal core modules is not advisable. Having the core modules modified makes it harder to migrate to newer versions of drupal.
But certain unavoidable circumstances developers to modify the core modules. When these circumstances come, it would be very helpful to have proper documentation. It will keep track of the changes made.
I am now in a situation where I am hoping that there were documentations made.
Advance cache modules comes wtih lots of patches to be applied to the core modules. Wondering why the patches don’t apply cleanly, I investigated the modules and found out that these modules were edited sometime in the past.
I am now doing a task that takes a lot of time, a task that could have been avoided if only there were proper documentation, a task to sweep and search the whole core modules and see what changes have been done. And after finding the changes, investigate how those changes affect the system.
I’m writing this blog not to brag about what I’m doing nor to announce how I’m studying the drupal core, but to emphasize and remind every developer to make proper documentation in every code. In this way, it will be a lot easier for other other programmers to finish/continue/edit/modify previous programs.