protected function libStrInsert($args)
{
$string = $this->coerceString($args[0]);
$stringContent = $this->compileStringContent($string);
$insert = $this->coerceString($args[1]);
$insertContent = $this->compileStringContent($insert);
list(, $index) = $args[2];
$string[2] = [substr_replace($stringContent, $insertContent, $index - 1, 0)];
return $string;
}