Q:

What does "All examples have been tested directly from the text, which is in machine-readable form" mean?

I am reading the classic book on C - The C Programming Language
Book by Brian Kernighan and Dennis Ritchie. The preface of the book says

All examples have been tested directly from the text, which is in machine-readable form. 

What does this mean?

A:

(just a guess)
Probably that every code example has been indeed tested on a system with a C compiler, and pretty-printed in the book (perhaps using troff or whatever document formatter was used by K&R) by some automatic tool (I don't know what tool was used by K&R. Today, you'll use e.g. vgrind or pygments or LaTeX's listings package, or some other pretty-printer). So there cannot be typos while converting C code to paper (e.g. as if the C code has been manually copied and typeset)

