A virtual field text search predicate filters the documents containing keywords in a specific virtual field chosen while indexing the corpus. Building a virtual field text search predicate involves calling the built-in vfts function that takes two string arguments, representing respectively the name of the virtual field, and the keywords of the query.
The semantics for the keywords of the query is the same as the semantics of full-text search predicates. In particular, the keywords are standardized by AFS before their evaluation — this standardization replaces each keyword by its lowercase, without accents, value —, and the syntax for an expression search is the same.
For example, vfts("author", "foo") returns the document with the virtual field "author" containing "foo".
For example, vfts("type", "’search engine’") only returns documents containing the exact expression "search engine" in their "type" virtual field.
The query can also be expressed with vfts("type", "\"search engine\"").