https://invisible-island.net/xterm/xtoolkit/
XtVaCreateArgsList - dynamically allocate a varargs list
#include <X11/Intrinsic.h>
XtVarArgsList XtVaCreateArgsList(XtPointer unused, ...);
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 argu-
ments into a single list pointer, which may be used with XtVaNest-
edList. 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
X Version 11 libXt 1.1.5.2 XtVaCreateArgsList(3)