> For the complete documentation index, see [llms.txt](https://docs.b2ihealthcare.com/snow-owl-authoring-platform/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.b2ihealthcare.com/snow-owl-authoring-platform/7.19.0/browsing-and-searching/semantic-queries/project-explorer-view/expression-file/validation.md).

# Validation

Queries are validated continuously as you enter the expression. Erroneous parts of the expression are indicated with a red wavy underline, as well as a red error marker ![](https://904483993-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2Fso-user-guide%2F-M286ZsHNIoKac3m-EVl%2F-M286fKxzkhS0-QC4mw0%2F611025873.png?generation=1583922227760624\&alt=media) on the left margin of the editor.

Expression Constraint Language (ECL) queries are also validated to check for inactive concepts that are referenced in the expression. As the editor only allows the selection or insertion of active concepts through the concept picker, this feature helps in identifying concepts that became inactive after the expression was authored.

![Inactive Reference Warning in ECL Editor](https://904483993-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcgelYf9y6IT26ZqjUpeU%2Fuploads%2FzwnsoziWQigfRz1kyniy%2Fecl_validation.png?alt=media\&token=c912bf16-1144-4b5d-b127-b9aac7290e59)