Difference in gcc -ffp-contract options

I have a question regarding the -ffp-contract flag in GNU GCC (see https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html).

The flag documentation is written as follows:

-ffp-contract=off disables floating-point expression contraction. -ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. -ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp-contract=off. The default is -ffp-contract=fast.

Now the question:

• What is the difference between fast and on?
• Is there any other contraction example beside the FMA (or similar like the fused-mult sub)?