XtVaCreateArgsList man page
XtVaCreateArgsList — dynamically allocate a varargs list
XtVarArgsList XtVaCreateArgsList(XtPointer unused, ...);
Must be specified as NULL.
Specifies a variable parameter list of resource name and value pairs.
The XtVaCreateArgsList function allocates memory and copies its arguments into a single list pointer, which may be used with XtVaNestedList. The end of both lists is identified by a name entry containing NULL. Any entries of type XtVaTypedArg are copied as specified without applying conversions. Data passed by reference (including Strings) are not copied, only the pointers themselves; the caller must ensure that the data remain valid for the lifetime of the created varargs list. The list should be freed using XtFree when no longer needed.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface