Miscellaneous

if($condition, $if-true, $if-false) Returns one of two values, depending on whether or not $condition is true.
unique-id() Returns a unique CSS identifier.
'if' must immediately be followed by '(' without any space in between.
div:after {
   content: if((2 > 1), unique_id(), hello);
}

div:after {
  content: u06j4m5bl;
}