Function is_escaped_str 

pub fn is_escaped_str(unescaped_str: &str) -> bool

Checks if an input string is already escaped. The idea is to avoid escaping the escaped string thus making it a nightmare to undo the escaping later on.

Basically, if you were to blindly escape the input string, back slashes keep getting escaped. For example \r -> \\r -> \\\\r -> ....