Updated Developer documentation (markdown)

Developer-documentation.md

@@ -28,6 +28,19 @@ Each error type must have a status code that is unique in the whole program. The
 - First 4 bits: identifies a certain module of the previewer
 - Last 4 bits: identifies the exact problem
 
+## Memory allocation
+
+The module provides its own memory allocation library called **MagicMemory**. The library can be used to create MagicMemory contexts. All memory allocation calls must be performed through this library. If a function allocates memory, it has to take a MagicMemory context (that has the type `mm_ctx`) as its first parameter and perform the memory allocation inside that context. Before the program exits, all of the contexts must be freed up.
+
+## Data validation
+
+There are two different kinds of functions that perform data validation:
+
+- **Validator**: A validator only validates data according to its format specification.
+- **Parser**: A parser validates data and then extracts some fields from the data.
+
+It is not unusual for a parser function to call a validator function to validate its whole input before extracting the fields.
+
 # CAFF previewer wrapper
 This module makes communication between the previewer and the web client possible.