And is it only about the format or also about the behavior of the types under common mathematical operations?
And format (as I think was mentioned) can be storage format or range of mantissa and exponent.



I don't know what "It" means. The spec does define conversion from wider floating point types and describes saturating and non-saturating modes.
So, one could perform common mathematical operations in infinite precision and then narrow the result to quarter precision. However, I don't see that described.

The spec "provides two binary interchange formats for floating point encodings."