How do I populate a WPF Combobox with XPath queries stored in a file?

Question

I have two files -- the first (data) is an XML document, and the second (queries) contains XPath queries I would like to run on the first document.

I would like to populate a combobox in WPF to the queries, so that it displays the names of the XPath queries. When the user selects an item in the combobox, it should populate a listbox with selected nodes in the data document.

I have working code for the 2nd part (populating the listbox with a hard-coded XPath query), I just need to make it selectable. Here is the snippet of code I have working (minus the static resources, etc).

added on 1 Oct 2009

I've been staring at this for a bit, and I've broken down the problem into two key parts:

1. I want the combobox to contain XPath queries that will populate the listbox (when I select a combobox item, it should update the listbox with valid entries from the XML document).
2. I would like to load the queries for the combobox from a file. This way, users can add their own queries, and not have to recompile the application.

I've solved the first problem, and the code below is updated to reflect this.

<Grid  Name="MainGrid" DataContext="{Binding Source={StaticResource xmldoc}}">
    <ComboBox Height="23" Margin="0,1,0,0" Name="comboBox1" VerticalAlignment="Top">
        <ComboBoxItem DataContext={Binding XPath=/find/something}">Query Name</ComboBoxItem>
        <ComboBoxItem DataContext={Binding XPath=/find/something/else}">Other Query Name</ComboBoxItem>
    </ComboBox>

    <ListBox Height="100" Name="listBox1" VerticalAlignment="Top"
             ItemsSource="{Binding ElementName=comboBox1, Path=SelectedItem.DataContext}"
             ItemTemplate="{StaticResource listTemplate}" Margin="0,30,0,0" />

    <TextBox Margin="0,136,0,29" DataContext="{Binding ElementName=listBox1, Path=SelectedItem}"
             Text="{Binding XPath=.}" />
</Grid>

The key hear is the ItemsSource for listBox1: I originally tried to make Path=SelectedItem (as I did for TextBox), but it never worked. if you make the path the DataContext of the selected item, however, it works great.

This, of course, still leaves the second part: how do I load these queries from a separate file?