This built-in module is available from the URL sass:string.
index($string, $substring)
This function is also available as a global function named str-index().
insert($string, $insert, $index)
This function is also available as a global function named str-insert().
length($string)
This function is also available as a global function named str-length().
quote($string)
This function is also available as a global function named quote().
slice($string, $start-at, $end-at: -1)
This function is also available as a global function named str-slice().
to-lower-case($string)
This function is also available as a global function named to-lower-case().
to-upper-case($string)
This function is also available as a global function named to-upper-case().
unique-id()
This function is also available as a global function named unique-id().
unquote($string)
This function is also available as a global function named unquote().