public function allowExtensions($extensions)
    {
        if (!is_array($extensions)) {
            $extensions = [$extensions];
        }
        $this->constraints[] = new ExtensionConstraint($extensions);
        return $this;
    }
public function allowExtensions($extensions)
    {
        if (!is_array($extensions)) {
            $extensions = [$extensions];
        }
        $this->constraints[] = new ExtensionConstraint($extensions);
        return $this;
    }
public function allowExtensions ( $ extensions ) { if ( ! is_array ( $ extensions ) ) { $ extensions = [ $ extensions ] ; } $ this -> constraints [ ] = new ExtensionConstraint ( $ extensions ) ; return $ this ; }
Set allowed extensions

@param array|string $extensions
@return $this
Set allowed extensions