diff --git a/TinyFrame.c b/TinyFrame.c
index be69d8e..36baaa3 100644
--- a/TinyFrame.c
+++ b/TinyFrame.c
@@ -36,6 +36,7 @@
 
 #elif TF_CKSUM_TYPE == TF_CKSUM_CRC16
 
+// TODO try to replace with an algorithm
 /** CRC table for the CRC-16. The poly is 0x8005 (x^16 + x^15 + x^2 + 1) */
 static const uint16_t crc16_table[256] = {
     0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
@@ -83,6 +84,7 @@ static inline uint16_t crc16_byte(uint16_t cksum, const uint8_t byte)
 
 #elif TF_CKSUM_TYPE == TF_CKSUM_CRC32
 
+// TODO try to replace with an algorithm
 static const uint32_t crc32_table[] = { /* CRC polynomial 0xedb88320 */
     0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
     0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
diff --git a/TinyFrame.h b/TinyFrame.h
index 1ab704a..4bb5551 100644
--- a/TinyFrame.h
+++ b/TinyFrame.h
@@ -91,6 +91,7 @@ typedef enum {
     TF_MASTER = 1,
 } TF_Peer;
 
+/** Response from listeners */
 typedef enum {
     TF_NEXT = 0,   //!< Not handled, let other listeners handle it
     TF_STAY = 1,   //!< Handled, stay
@@ -132,6 +133,8 @@ typedef TF_Result (*TF_Listener)(TinyFrame *tf, TF_Msg *msg);
 
 // -------------------------------------------------------------------
 
+// region Internal
+
 enum TFState_ {
     TFState_SOF = 0,      //!< Wait for SOF
     TFState_LEN,          //!< Wait for Number Of Bytes
@@ -207,11 +210,19 @@ struct TinyFrame_ {
     uint8_t sendbuf[TF_SENDBUF_LEN];
 };
 
+// endregion
+
 // -------------------------------------------------------------------
 
 /**
  * Initialize the TinyFrame engine.
- * This can also be used to completely reset it (removing all listeners etc)
+ * This can also be used to completely reset it (removing all listeners etc).
+ *
+ * The field .userdata (or .usertag) can be used to identify different instances
+ * in the TF_WriteImpl() function etc. Set this field after the init.
+ *
+ * This function is a wrapper around TF_InitStatic that calls malloc() to obtain
+ * the instance.
  *
  * @param peer_bit - peer bit to use for self
  */
@@ -221,6 +232,8 @@ TinyFrame *TF_Init(TF_Peer peer_bit);
 /**
  * Initialize the TinyFrame engine using a statically allocated instance struct.
  *
+ * The .userdata / .usertag field is preserved when TF_InitStatic is called.
+ *
  * @param peer_bit - peer bit to use for self
  */
 void TF_InitStatic(TinyFrame *tf, TF_Peer peer_bit);