You define dialog boxes by entering DCL descriptions in ASCII text files, much like writing AutoLISP code. DCL files have a .dcl extension. A single DCL file can contain the description of one or more dialog boxes, or it can contain only prototype tiles and subassemblies for use by other DCL files. A DCL file consists of the following three parts, which can appear in any order. Depending on your application, only one or more of these parts is required.
These are tile definitions you can refer to in subsequent tile definitions (including dialog box definitions).
These define the attributes of tiles or override the attributes defined in prototype tiles and subassemblies.