A string slice is a reference to a sequence of bytes in memory that must always be valid utf-8.
A string slice (a sub-slice) of a str slice, must also be valid utf-8.
Common methods of &str:
len gets the length of the string literal in bytes (not number of characters).starts_with/ends_with for basic testing.is_empty returns true if zero length.find returns an Option<usize> of the first position of some text.