input = {
  [[digit ::= "0"..."9"]],
  [[lowercase ::= "a"..."z"]]
}
output = {
  {"digit", "lowercase"},
  " ::= \"",
  {"0", "a"},
  "\"...\"",
  {"9", "z"},
  "\""
}

Note that there IS some guess work involved.

For example, if "digit" and "lowercase" had common characters, a differ might see these characters as a common part of both texts.

So we assume some heuristics like keeping words in one piece. Those heuristics may or may not apply for a given task.