ItsyBitsy M0 Express

My UNO based programs doing Serial I/O don't compile on the Itsy because "SoftwareSerial.h" is not found.
I'm having trouble understanding the Adafruit advice on how to migrate older programs to the M0 boards.
I'm wondering if I can just use the old "SoftwareSerial.h" or can someone point me to some example code for the M0 board I'm using?

Hi RayL,

I believe's (when Arduino was split into two rival entities) M0 library included software serial. That was back in 2016/2017, however the code has since been removed from Github.

In any case, it's usually not necessary to use software serial with the M0, as it's possible to configure its spare serial communication (or SERCOM) modules to become additional hardware serial ports instead.

Adafruit has a tutorial on configuring the spare SERCOM modules for Serial, I2C or SPI. Here's a link to the serial configuration web page: Creating a new Serial | Using ATSAMD21 SERCOM for more SPI, I2C and Serial ports | Adafruit Learning System.