The --search-common-action-filter-on-expr and --search-common-action-filter-out-expr parameters are both CEL programs.
NOTE: They filter what gets indexed into search. They are not a language you can use to query the indexes.
CEL is Google's Common Expression Language:
The same list of identifiers available for searching in dfuse Search is available for filtering.
For example, a dfuse Search of:
receiver:eosio.token data.from:bob
would be filtered as:
receiver == 'eosio.token' && data.from == 'bob'
See https://docs.dfuse.io/reference/eosio/search-terms/ for all EOSIO terms that can be filtered.