AutoLISP application files contain custom commands and functions from the user interface, and must be loaded before they can be used.
The program automatically loads MNL files with the same name and location as your main, enterprise, or partial customization (CUIx) files. Additional AutoLISP (LSP) files can be loaded with a CUIx file by adding a reference to the file under the LISP Files node displayed for a loaded CUIx file in the Customizations In pane of the Customize User Interface (CUI) Editor.