The most horrific thing I discovered about tcl is that curly braces within comments can affect flow control. This is because comments are interpreted as a command that does nothing, not the same as complete ignored. Finding that out the hard way was not fun.
This is not true. Once Tcl sees a valid comment, the rest of the line up to the newline is treated as a comment. An odd number of trailing backslashes suppress the newline for interpretation purposes. Within the comment you can use braces or whatever without affecting control flow.
However, the parser is confused by unbalanced braces in comments.
Here's a classic case that turns up occasionally during development:
proc asdf { args } {
# if { first draft complex condition } {
if { final simplified condition } {
do something
} else {
do something else
}
}
missing close-brace: possible unbalanced brace in comment