It is an option on the Advanced Properties of the Control called - tabindex.
Each frame appears to have it's own tab index along with each Frame also
having their own tab index
frame1 - tabindex 1
frame2 - tabindex2
etc.
control1 - tabindex1
control2 - tabindex2
etc.
If you set the tabindex to 0 it will not be included in the tab order
sequence