Due to the way the Tcl language parser works, braces in the code must be properly matched. This includes the braces in comments.
proc hw {} {
# this { code will fail
puts {hello world}
}
A missing close-brace: possible unbalanced brace in comment error will be thrown.
proc hw {} {
# this { comment } has matching braces.
puts {hello world}
}
This will work as the braces are paired up properly.