FlowDocument replace Section?

I have a FlowDocument with two Sections. One is named 'Inhalt'.

Trying to replace it with another Section d开发者_如何学编程oesn't seem to work:

        InfoBoxAuditorium.Inhalt = InfoBoxAuditorium.Resources["DokumentWohnzimmer"] as Section;

What am I doing wrong?

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Just for the records. I solved this by surrounding the FlowDocument with another Grid. The first row contains the stuff I don't want to be replaced. Easy but it does its job.