"AND", "OR" syntax in Query Parameter "finder"

Summary:

By means of REST API, I am trying to get all suppliers with site(s) assignment having "Bill-to BU" for example "bu_1" (buid: 123) or "bu_2" (buid: 456).

Content (required):

Data Example:

Supplier_1: site_1: bill-to-bu = "bu_1"

Supplier_2: site_1: bill-to-bu = "bu_2"

Supplier_3: site_1: bill-to-bu = "bu_1" + bill-to-bu = "bu_2"

Supplier_4: site_1: bill-to-bu = "bu_3"

Case 1:

# As tried, the filter criteria means "bu_1" AND "bu_2", REST call returns Supplier_3.

https://<server_name>/fscmRestApi/resources/11.13.18.05/suppliers?finder=FindByBilltoBU;BilltoBuId=123,BilltoBuId=456

Case 2:

# As tried, the filter criteria means "bu_1" OR "bu_2", REST call returns Supplier_1, Supplier_2, Supplier_3.

https://<server_name>/fscmRestApi/resources/11.13.18.05/suppliers?finder=FindByBilltoBU;BilltoBuId=123,456

Question:

Is there any document explaining syntax of "finder" in query parameter?