Which pins are represented by these constants from ABR library? The following code comes from AtTiny serial library that I want to use:

#include &lt;avr/io.h&gt;
#include &lt;avr/interrupt.h&gt;
#include &lt;util/delay.h&gt;

// change these to use another pin
#define TX_PORT PORTB
#define TX_PIN  PB0
#define TX_DDR  DDRB
#define TX_DDR_PIN DDB0


I have no idea which pins to connect. What do these constants mean and where are they documented?
The mapping can be found in the io.h file but also in Arduino core files.

Below is the pin mapping:

                        ATtinyX4
                      +----U----+
  (VCC)-------------1-|VCC   GND|-14------------(GND)
  (D10)-------------2-|PB0   PA0|-13----------(D0/A0)
  (D9)--------------3-|PB1   PA1|-12----------(D1/A1)
  (/RESET)----------4-|PB3   PA2|-11----------(D2/A2)
  (D8)--------------5-|PB2   PA3|-10-------(D3/A3/SS)
  (D7/A7)-----------6-|PA7   PA4|-9---(D4/A4/SCL/SCK)
  (MISO/SDA/D6/A6)--7-|PA6   PA5|-8------(D5/A5/MOSI)
                      +---------+


The serial library uses:

#define TX_PIN  PB0


Which is ATtinyX4 Pin #2, or Arduino attiny core digital pin D10 https://github.com/damellis/attiny/blob/master/variants/tiny14/pins_arduino.h. 

Cheers