ecore_imf_context_retrieve_surrounding_callback_set () is very important to input languages such as Thai.
*
* This callback will be called when the Input Method Context
* module requests the surrounding context.
+ * Input methods typically want context in order to constrain input text based on existing text;
+ * this is important for languages such as Thai where only some sequences of characters are allowed.
*
* @param ctx An #Ecore_IMF_Context.
* @param func The callback to be called.