+* `SPLIT_TRANSPORT = custom`
+ * Allows replacing the standard split communication routines with a custom one. ARM based split keyboards must use this at present.
+
+### Setting Handedness
+
+One thing to remember, the side that the USB port is plugged into is always the master half. The side not plugged into USB is the slave.
+
+There are a few different ways to set handedness for split keyboards (listed in order of precedence):
+
+1. Set `SPLIT_HAND_PIN`: Reads a pin to determine handedness. If pin is high, it's the left side, if low, the half is determined to be the right side
+2. Set `EE_HANDS` and flash `eeprom-lefthand.eep`/`eeprom-righthand.eep` to each half
+ * For boards with DFU bootloader you can use `:dfu-split-left`/`:dfu-split-right` to flash these EEPROM files
+ * For boards with Caterina bootloader (like stock Pro Micros), use `:avrdude-split-left`/`:avrdude-split-right`
+3. Set `MASTER_RIGHT`: Half that is plugged into the USB port is determined to be the master and right half (inverse of the default)
+4. Default: The side that is plugged into the USB port is the master half and is assumed to be the left half. The slave side is the right half
+
+#### Defines for handedness
+