LZ followed by entropy coding seems to be the general strategy of choice for many compression algorithms, so this design of Zstandard was quite familiar to me. The FSE reminded me of the Q/MQ/QM-coder algorithm which is used in some image formats (and is surprisingly simple yet powerful, although relatively slow.)
Nonetheless, I like to learn a file format by studying a worked example at the bits and bytes level.
I did the same when I was playing around with various image and video codecs (JPEG, GIF, MPEG-1/2, etc.), and I agree that it definitely helps with understanding as well as debugging; you can get to the point of being able to decode, slowly, by just staring at a hexdump and "reading" the bits and bytes as if it was a new language.
Nonetheless, I like to learn a file format by studying a worked example at the bits and bytes level.
I did the same when I was playing around with various image and video codecs (JPEG, GIF, MPEG-1/2, etc.), and I agree that it definitely helps with understanding as well as debugging; you can get to the point of being able to decode, slowly, by just staring at a hexdump and "reading" the bits and bytes as if it was a new language.