the [2,2,3,2,3] are array of values for example $2,$2$3,$2,$3
the 4 is periods 
$t=trader_rsi ( [2,2,3,2,3],4);
print_r($t);
returns :
Array ( [4] => 66.667 )
    (PECL trader >= 0.2.0)
trader_rsi — Relative Strength Index
$real
   , int $timePeriod = ?
   ) : array
real浮点数数组。
timePeriodNumber of period. Valid range from 2 to 100000.
Returns an array with calculated data or false on failure.
the [2,2,3,2,3] are array of values for example $2,$2$3,$2,$3
the 4 is periods 
$t=trader_rsi ( [2,2,3,2,3],4);
print_r($t);
returns :
Array ( [4] => 66.667 )