Xadefault.h includes the library functions, which are necessary for the Motif environment, and declares the widgets and global variables. Most of the widgets are defined as arrays whose element names are declared as enumerated lists.
Xadefault.h also reads in Default.h which includes the standard C libraries and the modules which are necessary for the creation and access of orbital data but not for the graphical user interface. Default.h also defines the global labels, like the error return codes or MAX_STRING_LEN, which are used in the source code to avoid inconsistencies in case of changes in these basic variables.