TestWrap

local function wrap(str, limit)
  local Lines, here, limit = {}, 1, limit or 72
  Lines[1] = string.sub(str,1,str:find("(%s+)()(%S+)()")-1)  -- Put the first word of the string in the first index of the table.

  str:gsub("(%s+)()(%S+)()",
        function(sp, st, word, fi)  -- Function gets called once for every space found.
          if fi-here > limit then
                here = st
                Lines[#Lines+1] = word                                             -- If at the end of a line, start a new table index...
          else Lines[#Lines] = Lines[#Lines].." "..word end  -- ... otherwise add to the current table index.
        end)

  return Lines
end

local myText = "THIS IS A REALLY LONG TEXT THAT I WOULD LIKE TO WRAP AT A CERTAIN MARGIN."

local myTable = wrap(myText,20)

for k,v in pairs(myTable) do print(k.." = "..v) end