I have code like this
<RichTextBox IsDocumentEnabled="True" Name="doc">
<FlowDocument>
    <Section>
        <BlockUIContainer>
            <StackPanel>
                <Image Height="30" Width="30" HorizontalAlignment="Left" Source="Notify.png">
                </Image>
                <TextBlock Text="message body">
                </TextBlock>
            </StackPanel>
        </BlockUIContainer>
    </Section>
    <Section>
        <Paragraph Margin="0,0,500,0" LineHeight="50">
            <Paragraph.Background>
                <ImageBrush ImageSource="bg1.png" Stretch="UniformToFill"/>
            </Paragraph.Background>
            test pure document text 
        </Paragraph>
        <Paragraph>
            <Run>
                <Run.Background>
                    <ImageBrush ImageSource="bg1.png"/>
                </Run.Background>
                run back groud,run back groud,run back groudrun back groudrun back groudrun back groudrun back groudrun back groudrun back groudrun back groudrun back groud
            </Run>
        </Paragraph>
    </Section>
<FlowDocument>
in this RichTextBox control , I add a control element and a document element. I could freely select text from the document element, while could not do it for UI control element.
Second part.
I wana set a Run element background like a control or container do. in above picture , the text block " run back groud,..." background is a little strange.
what effect I need is below. 

Any Idea? thanks

