# ECL examples

The [Expression Constraint Language - Specification and Guide](broken://spaces/sOJBD7YbxAy9bD1Ko9L9/pages/V7TAAramwXseIdqJEzP6) provides detailed background and further information on ECL. Its Appendices contain many examples of expressions, covering both valid and invalid expressions, direct aliases and Reference Set fields, as well as an ECL Quick Reference:

* [Appendix A - Examples of Valid Expressions](/snomed-ct-specifications/snomed-ct-expression-constraint-language/appendices/appendix-a-examples-of-valid-expressions.md)
* [Appendix B - Examples of Invalid Expressions](/snomed-ct-specifications/snomed-ct-expression-constraint-language/appendices/appendix-b-examples-of-invalid-expressions.md)
* [Appendix C - Direct Aliases](/snomed-ct-specifications/snomed-ct-expression-constraint-language/appendices/appendix-c-dialect-aliases.md)
* [Appendix D - ECL Quick Reference](/snomed-ct-specifications/snomed-ct-expression-constraint-language/appendices/appendix-d-ecl-quick-reference.md)
* [Appendix E - Reference Set Fields](/snomed-ct-specifications/snomed-ct-expression-constraint-language/appendices/appendix-e-reference-set-fields.md)

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