src/HtmlElementAbstract.php
public function appendAttribute($key, $value = null, $seperater = null)
    {
        if (!is_null($value)) {
            if ($this->getAttributeMap()->hasKey($key)) {
                if (strlen($seperater) > 0) {
                    $values = array();
                    $values[] = $this->getAttributeMap()->get($key);
                    $values[] = $value;
                    $newValue = implode($seperater, $values);
                } else {
                    $newValue = $this->getAttributeMap()->get($key) . $value;
                }
            } else {
                $newValue = $value;
            }
            $this->getAttributeMap()->set($key, $newValue);
        }
        return $this;
    }
public function appendAttribute($key, $value = null, $seperater = null)
    {
        if (!is_null($value)) {
            if ($this->getAttributeMap()->hasKey($key)) {
                if (strlen($seperater) > 0) {
                    $values = array();
                    $values[] = $this->getAttributeMap()->get($key);
                    $values[] = $value;
                    $newValue = implode($seperater, $values);
                } else {
                    $newValue = $this->getAttributeMap()->get($key) . $value;
                }
            } else {
                $newValue = $value;
            }
            $this->getAttributeMap()->set($key, $newValue);
        }
        return $this;
    }
append attribute to html element

@param       string      $key        html element attribute key
@param       string      $value      html element attribute value
@param       string      $seperater  html element attribute seperater
@return      HtmlElementAbstract