TextRange.Contains Method

// This method returns true if two specified selections overlap, including when the
// end of one selection serves as the beginning of the other.
bool DoSelectionsOverlap(TextRange selection1, TextRange selection2)
{
    // Is either end of selection2 contained by selection1?
    if (selection1.Contains(selection2.Start) || selection1.Contains(selection2.End))
    {
        // If so, the selections overlap.
        return true;
    }
    // If not, selection2 may still entirely contain selection1.
    // Is either end of selection1 contained by seleciotn2?
    else if (selection2.Contains(selection1.Start) || selection2.Contains(selection1.End))
    {
        // If so, the selections overlap.
        return true;
    }
    // If neither selection contains the begging or end of the other selection, 
    //the selections do not overlap.
    else return false;    
}