Is Lua 5.2's implementation/specification of weak tables compatible with Lua 5.1's specification?

["Soni L." <fakedme@...>]

From reading the specs for Lua 5.2: 
http://www.lua.org/manual/5.2/manual.html#2.5.2 and Lua 5.1: 
http://www.lua.org/manual/5.1/manual.html#2.10.2 it seems that Lua 5.2's 
implementation is compliant with Lua 5.1's specification. That is, Lua 
5.2 simply defines what in Lua 5.1 is undefined.

Can/should a Lua 5.1 interpreter use Lua 5.2's weak table behaviour? 
(namely, ephemeron tables)

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