vm/ops.go
func txUnmarkRaw(st *State) {
	if reflect.ValueOf(st.sa).Type() == rawStringType {
		st.sa = string(interfaceToString(st.sa))
	}
	st.Advance()
}
func txUnmarkRaw(st *State) {
	if reflect.ValueOf(st.sa).Type() == rawStringType {
		st.sa = string(interfaceToString(st.sa))
	}
	st.Advance()
}
// Sets the contents of register sa to a regular string, and removes
// the "raw string" mark, forcing html escapes to be applied when printing.
// Note that this effectively stringifies the contents of register sa