I'm trying to clip a reference drawing which is large tif file.  

I'm new to Draftsight, and can't sort out how to specify the referenced image in step 2 below.   Clicking on the image doesn't seem to work. 

I'm using Draftsight 2015 Free Mac.   

From...

http://www.aem-e.com/draftsight/html/hlpid_block_xclip.htm

To clip References or Blocks:

1. Click Modify > Clip > Reference (or type ClipReference).
2. Specify the References or Blocks to which you want to apply a clipping boundary, and press Enter.
3. Specify an option:

Thanks