Compass:

/**

• into: The target collection.
• on: Fields to identify.
• let: Defined variables.
• whenMatched: Action for matching docs.
• whenNotMatched: Action for non-matching docs.
  */ { into: 'negativeAccounts', on: 'string', let: 'specification(s)', whenMatched: 'string', whenNotMatched: 'string' }

Docs:

into: <collection> or { db: <db>, coll: <collection> },
on: <identifier field> or [ <identifier field1>, ...], // Optional
let: <variables>, // Optional
whenMatched: <replace|keepExisting|merge|fail|pipeline>, // Optional
whenNotMatched: <insert|discard|fail> // Optional
} }