src/ViewAbstract.php
public function addAttribute($key, $value = null)
    {
        if (is_array($key)) {
            return $this->setAttributes($key);
        }

        $key = Helpers::camelCase($key);

        if (is_array($this->attributes) && array_key_exists($key, $this->attributes)) {
            $this->attributes[$key] .= " $value";

            return $this;
        }

        $this->attributes[$key] = $value;

        return $this;
    }
public function addAttribute($key, $value = null)
    {
        if (is_array($key)) {
            return $this->setAttributes($key);
        }

        $key = Helpers::camelCase($key);

        if (is_array($this->attributes) && array_key_exists($key, $this->attributes)) {
            $this->attributes[$key] .= " $value";

            return $this;
        }

        $this->attributes[$key] = $value;

        return $this;
    }
@param string|array  $key
@param string|null   $value

@return $this