xtail usage is

xtail
[-b]		(output binary stream)
[-c xpath-expr]  (context; optional -- if not specified context is
assumed to be root)
[-e xpath-expr]  (element to tail)
[-n number] (num elements to tail if positive, num elements to head if
negative; optional -- default to 10)
[FILE]

-c and -e can be repeated many times

also, you can build xhead by "make -f makefile.xhead clean" then "make
-f makefile.xhead".  semantics are identical, except that the -n
parameters have sign reversed.
