This seems to me is referring to the historical
Thompson shell (Its successor Bourne Shell in UNIX v7 did not have a goto...)
1.
I think it means that you cannot use gotos if you use the shell interactively.
V6 Thompson Shell Port - Manuals - GOTO(1)
Presumably because there is a separate, external
goto command that needs to go look for the goto label, once invoked
2.
I would think that if the manual is explicit like that, only
: end would be allowed (
: being the first character on the line) with any number of spaces. The other label is maybe from another script, perhaps
sed ?
See also :
V6 Thompson Shell Port - Manuals - GOTO(1)
3.
Quote:
If such a line is found, goto repositions the command-file offset to the line after the label and exits
V6 Thompson Shell Port - Manuals - GOTO(1)
So it does seem that no commands will be processed on the line with the label.