split

local function splitWords(Lines, limit)
    while #Lines[#Lines] > limit do
        Lines[#Lines+1] = Lines[#Lines]:sub(limit+1)
        Lines[#Lines-1] = Lines[#Lines-1]:sub(1,limit)
    end
end

local function wrap(str, limit)
    local Lines, here, limit, found = {}, 1, limit or 72, str:find("(%s+)()(%S+)()")

    if found then
        Lines[1] = string.sub(str,1,found-1)  -- Put the first word of the string in the first index of the table.
    else Lines[1] = str end

    str:gsub("(%s+)()(%S+)()",
        function(sp, st, word, fi)  -- Function gets called once for every space found.
            splitWords(Lines, limit)

            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)

    splitWords(Lines, limit)

    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