dev.md: updated doc

doc/dev.md

@@ -23,6 +23,8 @@
     - [4.2.3. ```appendfile <source> <destination>```](#423-appendfile-source-destination)
     - [4.2.4. ```isdirempty <directory>```](#424-isdirempty-directory)
     - [4.2.5. ```patch_file <source> <destination> [VAR1 [VAR2 ...]]```](#425-patch_file-source-destination-var1-var2-)
+    - [4.2.6. ```tagfile <list_of_files>```](#426-tagfile-list_of_files)
+    - [4.2.7. ```file_exists <list_of_files>```](#427-file_exists-list_of_files)
   - [4.3. Other functionnalities](#43-other-functionnalities)
 - [5. The pkgman.sh file](#5-the-pkgmansh-file)
   - [5.1. Global dependencies](#51-global-dependencies)
@@ -272,6 +274,26 @@ variables, in the context of the *init.sh* execution.
 Source file must exists and not be empty. The function returns nothing
 useful.
 
+#### 4.2.6. ```tagfile <list_of_files>```
+That function add a tag to the first line of the given files. If one file
+allready exists, the added line will be in the form:
+
+``` # File automatically modified by init.sh on $(stdtime).```
+
+If it don't exists it is created with the line:
+
+```# File automatically generated by init.sh on $(stdtime).```
+
+It's not using the file selection system as our source file are not suposed to
+be modified directly. In consequence, you should always provide fully qualified
+path names to it.
+
+#### 4.2.7. ```file_exists <list_of_files>```
+That function check files existance within our file selection system. If one
+source file is missing it will return an error and stop execution. That function
+is logicaly massively used during check phase to verify all source files are in
+place.
+
 ### 4.3. Other functionnalities
 That file don't profide any other things that the previously listed functions.