[Haskell-cafe] what's the definition of "satisfy" and "<?>" ?

I cannot understand the following code very well as i donot know the definition of "satisfy" and "<?>". -- | Case-insensitive variant of Parsec's 'char' function. caseChar :: Char -> GenParser Char a Char caseChar c = satisfy (\x -> toUpper x == toUpper c) -- | Case-insensitive variant of Parsec's 'string' function. caseString :: String -> GenParser Char a () caseString cs = mapM_ caseChar cs <?> cs Would somebody mind to explain the code in detail ? Sincerely!