public function addReference($filename, $line = null)
    {
        $key = "{$filename}:{$line}";
        $this->references[$key] = [$filename, $line];

        return $this;
    }
public function addReference($filename, $line = null)
    {
        $key = "{$filename}:{$line}";
        $this->references[$key] = [$filename, $line];

        return $this;
    }
public function addReference ( $ filename , $ line = null ) { $ key = "{$filename}:{$line}" ; $ this -> references [ $ key ] = [ $ filename , $ line ] ; return $ this ; }
Adds a new reference for this translation.

@param string   $filename The file path where the translation has been found
@param null|int $line     The line number where the translation has been found

@return self
Adds a new reference for this translation .