XdbeQueryExtension - returns the version of DBE supported by the server.
#include <X11/extensions/Xdbe.h>
Status XdbeQueryExtension(
   Display *dpy,
   int *major_version_return,
   int *minor_version_return)
Sets major_version_return and minor_version_return to the major
  and minor DBE protocol version supported by the server. If the DBE library is
  compatible with the version returned by the server, this function returns
  non-zero. If dpy does not support the DBE extension, or if there was an
  error during communication with the server, or if the server and library
  protocol versions are incompatible, this function returns zero. No other Xdbe
  functions may be called before this function. If a client violates this rule,
  the effects of all subsequent Xdbe calls that it makes are undefined.
DBE, XdbeAllocateBackBufferName(), XdbeBeginIdiom(),
  XdbeDeallocateBackBufferName(), XdbeEndIdiom(),
  XdbeFreeVisualInfo(), XdbeGetBackBufferAttributes(),
  XdbeGetVisualInfo(), XdbeSwapBuffers().