DocumentMask

A set of field paths on a document. Used to restrict a get or update operation on a document to a subset of its fields. This is different from standard field masks, as this is always scoped to a Document, and takes in account the dynamic nature of Value.

JSON representation 
{
  "fieldPaths": [
    string
  ]
}
Fields
fieldPaths[]

string

The list of field paths in the mask. See Document.fields for a field path syntax reference.