Lua的_G表里有啥？

今天看xlua源码的时候发现了一个表 _G，如图所示：

那它到底啥呢？
应该是保存了lua所有用到的全局变量和局部变量

比如：

这三种用法是一样的

_G.print("测试")
_G["print"]("测试")
print("测试")

那里面到底有啥呢？
全部输出为：

function: 00007FFFFB9ECA60
setfenv function: 000001718A717510
rawset  function: 00007FFFFB9EC6B0
_VERSION    Lua 5.3
print   function: 0000016E8893FC90
_G  table: 000001718A716390
     |--load function: 00007FFFFB9ECA60
     |--setfenv function: 000001718A717510
     |--rawset function: 00007FFFFB9EC6B0
     |--_VERSION Lua 5.3
     |--print function: 0000016E8893FC90
     |--_G table: 000001718A716390
     |--getmetatable function: 00007FFFFB9EC4B0
     |--xpcall function: 00007FFFFB9EC0D0
     |--tostring function: 00007FFFFB9EC190
     |--rawequal function: 00007FFFFB9EC5B0
     |--coroutine table: 000001718A7177D0
     |--pcall function: 00007FFFFB9EC040
     |--type function: 00007FFFFB9EC7E0
     |--setmetatable function: 00007FFFFB9EC510
     |--pairs function: 00007FFFFB9EC8A0
     |--table table: 000001718A7179D0
     |--io table: 000001718A717C90
     |--tonumber function: 00007FFFFB9EC300
     |--CS table: 000001718A717490
     |--error function: 00007FFFFB9EC430
     |--next function: 00007FFFFB9EC840
     |--getfenv function: 000001718A717890
     |--assert function: 00007FFFFB9EBF10
     |--cast function: 0000016E88940AA0
     |--typeof function: 00000171739A7190
     |--math table: 000001718A717390
     |--select function: 00007FFFFB9EBF90
     |--debug table: 000001718A7175D0
     |--uint64 table: 000001718A7171D0
     |--string table: 000001718A717DD0
     |--template table: 000001718A717B50
     |--utf8 table: 000001718A717ED0
     |--package table: 000001718A716E50
     |--rawlen function: 00007FFFFB9EC600
     |--xlua table: 000001718A717E50
     |--loadfile function: 00007FFFFB9EC980
     |--os table: 000001718A717450
     |--dofile function: 00007FFFFB9EBE90
     |--ipairs function: 00007FFFFB9EC930
     |--collectgarbage function: 00007FFFFB9EC710
     |--base function: 000001718A717550
     |--rawget function: 00007FFFFB9EC660
     |--require function: 000001718A717310
getmetatable    function: 00007FFFFB9EC4B0
xpcall  function: 00007FFFFB9EC0D0
tostring    function: 00007FFFFB9EC190
rawequal    function: 00007FFFFB9EC5B0
coroutine   table: 000001718A7177D0
     |--create function: 00007FFFFB9ECF40
     |--resume function: 00007FFFFB9ECE90
     |--isyieldable function: 00007FFFFB9ED120
     |--wrap function: 00007FFFFB9ECFA0
     |--yield function: 00007FFFFB9ED010
     |--status function: 00007FFFFB9ED040
     |--running function: 00007FFFFB9ED150
pcall   function: 00007FFFFB9EC040
type    function: 00007FFFFB9EC7E0
setmetatable    function: 00007FFFFB9EC510
pairs   function: 00007FFFFB9EC8A0
table   table: 000001718A7179D0
     |--sort function: 00007FFFFB9F58D0
     |--remove function: 00007FFFFB9F5140
     |--unpack function: 00007FFFFB9F57E0
     |--move function: 00007FFFFB9F52C0
     |--pack function: 00007FFFFB9F5730
     |--insert function: 00007FFFFB9F4FB0
     |--concat function: 00007FFFFB9F5510
io  table: 000001718A717C90
     |--open function: 00007FFFFB9EEC70
     |--popen function: 00007FFFFB9EED50
     |--stdout file (00007FFFFBA4A908)
     |--lines function: 00007FFFFB9EE590
     |--read function: 00007FFFFB9EE690
     |--stdin file (00007FFFFBA4A8B0)
     |--stderr file (00007FFFFBA4A960)
     |--input function: 00007FFFFB9EEE80
     |--close function: 00007FFFFB9EEBD0
     |--write function: 00007FFFFB9EE760
     |--type function: 00007FFFFB9EEA90
     |--tmpfile function: 00007FFFFB9EEE00
     |--output function: 00007FFFFB9EEF10
     |--flush function: 00007FFFFB9EE9C0
tonumber    function: 00007FFFFB9EC300
CS  table: 000001718A717490
     |--System table: 000001718A718D90
     |--System.RuntimeType: -1546318608 table: 000001718A718050
error   function: 00007FFFFB9EC430
next    function: 00007FFFFB9EC840
getfenv function: 000001718A717890
assert  function: 00007FFFFB9EBF10
cast    function: 0000016E88940AA0
typeof  function: 00000171739A7190
math    table: 000001718A717390
     |--sin function: 00007FFFFB9EFE80
     |--sqrt function: 00007FFFFB9F02F0
     |--huge inf
     |--floor function: 00007FFFFB9F0030
     |--ceil function: 00007FFFFB9F00B0
     |--mininteger -9223372036854775808
     |--tan function: 00007FFFFB9EFEE0
     |--rad function: 00007FFFFB9F0480
     |--pi 3.1415926535898
     |--log function: 00007FFFFB9F0370
     |--fmod function: 00007FFFFB9F0130
     |--asin function: 00007FFFFB9EFF10
     |--abs function: 00007FFFFB9EFE10
     |--random function: 00007FFFFB9F05E0
     |--deg function: 00007FFFFB9F0440
     |--ult function: 00007FFFFB9F0320
     |--atan function: 00007FFFFB9EFF70
     |--modf function: 00007FFFFB9F0210
     |--randomseed function: 00007FFFFB9F0710
     |--maxinteger 9223372036854775807
     |--cos function: 00007FFFFB9EFEB0
     |--type function: 00007FFFFB9F0740
     |--acos function: 00007FFFFB9EFF40
     |--min function: 00007FFFFB9F04C0
     |--tointeger function: 00007FFFFB9EFFD0
     |--exp function: 00007FFFFB9F0410
     |--max function: 00007FFFFB9F0550
select  function: 00007FFFFB9EBF90
debug   table: 000001718A7175D0
     |--getmetatable function: 00007FFFFB9ED3A0
     |--getlocal function: 00007FFFFB9ED8B0
     |--traceback function: 00007FFFFB9EE390
     |--setmetatable function: 00007FFFFB9ED3E0
     |--setupvalue function: 00007FFFFB9EDBF0
     |--getuservalue function: 00007FFFFB9ED440
     |--upvalueid function: 00007FFFFB9EDC80
     |--getregistry function: 00007FFFFB9ED380
     |--getupvalue function: 00007FFFFB9EDB70
     |--upvaluejoin function: 00007FFFFB9EDD00
     |--setlocal function: 00007FFFFB9EDA20
     |--sethook function: 00007FFFFB9EDE20
     |--gethook function: 00007FFFFB9EE020
     |--debug function: 00007FFFFB9EE1A0
     |--getinfo function: 00007FFFFB9ED4D0
     |--setuservalue function: 00007FFFFB9ED480
uint64  table: 000001718A7171D0
     |--tostring function: 00007FFFFB9FF8E0
     |--divide function: 00007FFFFB9FF7C0
     |--remainder function: 00007FFFFB9FF870
     |--parse function: 00007FFFFB9FF830
     |--compare function: 00007FFFFB9FF760
string  table: 000001718A717DD0
     |--format function: 00007FFFFB9F1DF0
     |--gmatch function: 00007FFFFB9F1B00
     |--upper function: 00007FFFFB9F2570
     |--gsub function: 00007FFFFB9F1BC0
     |--find function: 00007FFFFB9F1AE0
     |--byte function: 00007FFFFB9F2DF0
     |--packsize function: 00007FFFFB9F1580
     |--reverse function: 00007FFFFB9F23F0
     |--len function: 00007FFFFB9F22E0
     |--match function: 00007FFFFB9F1AF0
     |--unpack function: 00007FFFFB9F1720
     |--pack function: 00007FFFFB9F27D0
     |--char function: 00007FFFFB9F13E0
     |--lower function: 00007FFFFB9F24A0
     |--sub function: 00007FFFFB9F2310
     |--rep function: 00007FFFFB9F2640
     |--dump function: 00007FFFFB9F14C0
template    table: 000001718A717B50
     |--execute function: 0000016E88940500
     |--compile function: 0000016E8893FB50
utf8    table: 000001718A717ED0
     |--offset function: 00007FFFFB9F64C0
     |--char function: 00007FFFFB9F63A0
     |--codes function: 00007FFFFB9F6640
     |--charpattern [