Serial receiving and sending

Dear all,

I have few questions about serial functions in arduino, they are highlighted in code:

#define LIN_SERIAL HardwareSerial // if LIN_SERIAL is defined as hardware serial then I cannot define UART anymore as hardware serial for teensy?

class Lin
void serialBreak(void);
// For Lin 1.X “start” should = 0, for Lin 2.X “start” should be the addr byte.
static uint8_t dataChecksum(const uint8_t* message, char nBytes,uint16_t start=0);
static uint8_t addrParity(uint8_t addr);

Lin(LIN_SERIAL& ser=Serial,uint8_t txPin=1); //ser=serial what this means in Arduino, ?
LIN_SERIAL& serial;// same with this line, what is the function of it?
uint8_t txPin; // isnt that pin allready defined by board
int serialSpd; // in bits/sec. Also called baud rate
uint8_t serialOn; // whether the serial port is "begin"ed or "end"ed. Optimization so we don’t begin twice.
unsigned long int timeout; // How long to wait for a slave to fully transmit when doing a “read”. You can modify this after calling “begin”
void begin(int speed);

// Send a message right now, ignoring the schedule table.
void send(uint8_t addr, const uint8_t* message,uint8_t nBytes,uint8_t =2); //how is the send function defined in arduino?

// Receive a message right now, returns 0xff if good checksum, # bytes received (including checksum) if checksum is bad.
uint8_t recv(uint8_t addr, uint8_t* message, uint8_t nBytes,uint8_t proto=2); // how is the recv function working in arduino, can I use Arduino alternatives for this line to recievce all bytes from bus


ser=serial what this means in Arduino, ?

The same as it means in C++. "ser" is a reference to a "LIN_SERIAL" object, and its default value is the "Serial" object.

 LIN_SERIAL& serial;// same with this line, what is the function of it?

It's a reference.