Remarks

require - includes Lua files from local folder. One difference between debug require and non debug one is that debug one includes from local directory only when it was run first time. as an example:

local x = require('reqme');
function mod:newRoom()
 local x = require('reqme');
 Isaac.DebugString( x);
end

will work both times because reqme was cached but just:

function mod:newRoom()
 local x = require('reqme');
 Isaac.DebugString( x);
end

will not work if reqme is in local folder.