::This is a label that acts as a comment
:: comment shown above is not documented as being a comment command, but it is a special case of a label that acts as a comment.
Caution: when labels are used as comments within a bracketed code block or
for command, the command processor expects every label to be followed by at least one command,
so when a jump is made to the label it will have something to execute.
cmd shell will try to execute the second line even if it is formatted as a label (and this causes an error):
( echo This example will fail :: some comment )
When working within bracketed code blocks it is definitely safer to use REM for all comment lines.