Return part of a string
The input string. Must be valid UTF-8.
Start position in default grapheme units. If $start is non-negative, the returned string will start at the $start'th position in $string, counting from zero. If $start is negative, the returned string will start at the $start'th grapheme unit from the end of string.
Length in grapheme units. If $length is given and is positive, the string returned will contain at most $length grapheme units beginning from $start (depending on the length of string). If $length is given and is negative, then that many grapheme units will be omitted from the end of string (after the start position has been calculated when a start is negative). If $start denotes a position beyond this truncation, false will be returned.
Returns the extracted part of string, or false on failure.