This standard is a jointly developed OGC and ISO TC/211 International Standard that describes an XML and Key Value Pairs (KVP ) encoding of a system neutral syntax for expressing projections, selection and sorting clauses collectively called a query expression.
Version
2.0
Conformance Statement
The service conforms with the standard as per Technical Constraints section of the current service description.
Reference
https://www.ogc.org/standards/filter/