Indentation in Lezer

I have a Lezer grammar that is working. Is recognizes these expressions:

expression {
  Modifier  | StackModifier | Keyword | NotText 
}

There is one word “background:” that can be a Modifier when indented and a keyword when not. What approach should I take to making Lezer understand the distinction. I have been looking at

but I was wondering if there was a way to do it in the grammar files without a tokenizer.

That really sounds like something that’s easier to do in a tokenizer.

Would it be advisable to remove “background:” from the grammar and have the tokenizer make the distinction alone?

Tokens are used by the grammar. I don’t see any useful way in which you’d tokenize something but don’t parse it.