Term.blit extension

Hey guys,
How could i implement a mask or an char for term.blit, to let him skip writing chars (that it doesn't edits the screen)?
Two examples:

term.blit(''Hello world!', 'ffffffffffff', '000000000000', '##	   #  ')
-- or
term.blit(''Hello world!', 'ffffffffffff', '##0000000#00')
--[[ Output:
  llo wo ld
--]]

I want to have the best performance.

Simply use a buffer to keep track of the current screen contents. Overwrite the sections of the buffer that need to change, then blit the entire line from the buffer for any lines that have changed.