CQL Grammar and ECQL Grammar have slightly different keywords set.
ECQL is an extension of CQL and therefore it includes additional capabilities and keywords, such as the
ID, IN and ILIKE as well as SRID for geometry markers and some more.
However, it drop some keywords initially available in CQL (such as EQ, NEQ, ... ) probably since they are not officially defined in OGC specification.
OLD CQL_FILTERs containing these keywords will fail with an "invalid CQL_FILTER value" exception when parsed by ECQL.toFilter method.
We can add those dropped keywords to ECQL grammar too.