PDFsharp & MigraDoc Foundation

Is it possible to select multiple list items in a PdfListBoxField?

I have walked through the elements checking list item values against the ones I want to set and can set the selectedIndex property when one matches - but this will only allow me to select a single value.

I looked at a form with several items selected and the value property held a pdfarray so I built an array and tried to set the value property to i,t but am told that value can only be set to a string.

Is there any way to select several items?

many thanks in advance