src/StringType.php
public function upperFirst()
    {
        $this->value = mb_strtoupper(mb_substr($this->value, 0, 1, 'UTF-8'), 'UTF-8') . mb_substr($this->value, 1, null, 'UTF-8');
        return $this;
    }
public function upperFirst()
    {
        $this->value = mb_strtoupper(mb_substr($this->value, 0, 1, 'UTF-8'), 'UTF-8') . mb_substr($this->value, 1, null, 'UTF-8');
        return $this;
    }
Uppercase first letter

@return this