Cannot search " (single double-quotation) with q

[darashi]

GCS returned 400 if " is searched.

At least, no error reported from ACS with this query. The response is like this:

{"rank":"-text_relevance","match-expr":"(label '\"')","hits":{"found":0,"start":0,"hit":[]},"info":{"rid":"90c9b0fdba3e834bf5a4adc5a44bb0213c6fda472737d9c72c83ead280a55a1ff45793bcc973b90f","time-ms":2,"cpu-time-ms":0}}

The index searched against does not have any record with " for searchable fields, so the response is consistent.
But it is uncertain what happens if some records have " in the index.

[kou]

" in '...' means phrase search start and end. bq translator reports error if end " doesn't exist.
(I was thinking that \" is the syntax for searching " itself.)
But ACS doesn't treat it as an error. Uhm...

[darashi]

This is JSON, so \" means just ".

By the way, " " " (double-quotation, space, double-quotation, space, double-quotation) is recognized as (label '" " "'). hmm...

{"rank":"-text_relevance","match-expr":"(label '\" \" \"')","hits":{"found":0,"start":0,"hit":[]},"info":{"rid":"90c9b0fdba3e834bf5a4adc5a44bb0212773c26d3da56b25db84d3e4380d8cc3b901be631836be64","time-ms":1,"cpu-time-ms":0}}

Ah, it doesn't say anything... We can not see how the argument of label was interpreted...