Custom link in Richtextbox

Question

I am creating a usercontrol derived from Richtextbox.

The world is [beautiful]

I want to do the following operations on it

1) When the user keys in the ] , I need to create a link.

I have written the following code for this.

a) Select the text , Select (4,7) b) Set the mask and its effect

    private void SetSelectionStyle(UInt32 mask, UInt32 effect)
    {
        ColorConverter Colour = new ColorConverter();


        CHARFORMAT2_STRUCT cf = new CHARFORMAT2_STRUCT();
        cf.cbSize = (UInt32)Marshal.SizeOf(cf);
        cf.dwMask =  CFM_LINK ; // mask
        cf.dwEffects = effect;
        cf.crTextColor = ColorTranslator.ToWin32(Color.Red);

        IntPtr wpar = new IntPtr(SCF_SELECTION);
        IntPtr lpar = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
        Marshal.StructureToPtr(cf, lpar, false);

        IntPtr res = SendMessage(Handle, EM_SETCHARFORMAT, wpar, lpar);

        Marshal.FreeCoTaskMem(lpar);
    }

With this code I have 2 problems

1) The selection stays even after the link has been created. 2) When I move the cursor, the link goes away

2) If the word beautiful is a) not in my dictionary - change the link colour to red b) in the dictionary change it to green

The CFM_LINK and CFM_COLOR is not working together .

Can somone help me in where am I going wrong

Thanks, Sujay