I'm working with some code that

Controls.Add("Forms.Checkbox.1")

What does the word "Forms" above indicate?

I know there are the controls which are created on a sheet-only via Toolbar
Forms;
There are also controls from the Control toolbar (onsheet or Userform
-Active Xtype).

Then sometimes I see in Code "MSForms"... How can I better understand and
figure these things out? Help!!