Index for header reference

[dkarlovi]

If there are multiple times the same header is used, allow to add a numeric designation, example

    /**
     * @XLS\HeaderReference(header="Status", index=0)
     */
    public $status;

    /**
     * @XLS\HeaderReference(header="Status", index=1)
     */
    public $statusLabel;

[dkarlovi]

Alternatively, something like

    /**
     * @XLS\ExpressionReference(expression="header('Status')[0]")
     */
    public $status;

    /**
     * @XLS\ExpressionReference(expression="header('Status')[1]")
     */
    public $statusLabel;