Earlier quoted context omitted.
Jumping from Kermit to ZModem was quite a revelation for this Muppets fan. I was so sad to find I'd been needlessly reducing my download speed just by going with the fuzzy green frog, when presented with all of the different download options.
What gets me is that ZModem-Resume had effective continuation of failed transfers _decades_ before HTTP got it right. The early days of the web drove me bonkers, having to start over with a long file that failed in the middle.
In the spec, yes. But since servers use Content-Encoding instead of Transfer-Encoding for on-the-fly compression, its unspecified now whether the byte offsets in the resumption refer to the compressed or uncompressed file. Result: Download resumption did not work reliably and got removed from browsers.