Add doc about magic constants __FILE__ and __DIR__

diff --git a/doc/Developer-How-To-Move-Classes-to-src.md b/doc/Developer-How-To-Move-Classes-to-src.md
index ec86f02025f01b1300460336f87dd6f266579bd8..25eb393721ca0f936946d4c0b62fa7d5cb9f2939 100644 (file)
--- a/doc/Developer-How-To-Move-Classes-to-src.md
+++ b/doc/Developer-How-To-Move-Classes-to-src.md
@@ -99,6 +99,9 @@ Howevever, this tool isn't bullet-proof, and a staging install of Friendica is r
 
 Most of Friendica processes are run in the background, so make sure to turn on your debug log to check for errors that wouldn't show up while simply browsing Friendica.
 
+Check the class file for any magic constant `__FILE__` or `__DIR__`, as their value changed since you moved the class in the file tree.
+Most of the time it's used for debugging purposes but there can be instances where it's used to create cache folders for example.
+
 ## Related
 
 * [Class autoloading](help/autoloader)