New feature in #Tcl9 – part 37:

expr – supports comments inside expressions

Now this is really handy! Use this do properly document your overly long expressions easily:

expr {
# compute the sum of everything:
$myNumber + acos(-1) # acos(-1) = PI !
+ 34/double($myNumber) # the 34 is my invention ...
}

Note, that this is not a comment within double quotes or braces ...