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Work in progress on FHIR-50831. Needs the next version of the CQL spe… #74

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brynrhodes merged 1 commit into from
Aug 5, 2026
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Work in progress on FHIR-50831. Needs the next version of the CQL spe… #74

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1 change: 1 addition & 0 deletions input/pages/conformance.md
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Expand Up @@ -36,6 +36,7 @@ In addition to the use of CQL directly in [expression-valued elements](#using-ex

3. CQL library source files **SHOULD** be named `<CQLLibraryName>-<version>.cql`.
4. To avoid issues with characters between web ids and names, library names **SHALL NOT** have underscores.
5. Library.subject **SHALL** correspond to the context declaration in the CQL library

The prohibition against underscores in CQL library names is required to ensure compliance with the canonical URL pattern (because URLs by convention should not use underscores). In addition, many publishing environments will use the canonical tail (i.e. the name of the library) as the logical id of the Library resource, which does not allow underscores per the FHIR specification.

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16 changes: 16 additions & 0 deletions input/pages/using-cql.md
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Expand Up @@ -152,6 +152,22 @@ using FHIR version '4.0.1'

Snippet 2-3: Data Model line from [Example.cql](Library-Example.html#cql-content)

#### Context Declarations
{: #context-declarations}

CQL supports a `context` declaration that allows expressions to be evaluated with respect to a particular context, as defined by the data model being used. For FHIR-based models, the most common context is the `Patient` context, which is roughly analogous to the `Patient` compartment, but the FHIR ModelInfo defines a context for each `ComparmentDefinition` in the base specification.

**Conformance Requirement 2.5.1 (Context Declarations):** [<img src="conformance.png" width="20" class="self-link" height="20"/>](#conformance-requirement-2-5-1)
{: #conformance-requirement-2-5-1}

1. Libraries that use FHIR-based models **SHALL** specify at most one context declaration
2. If present, the context declaration **SHALL** be the first statement declaration in the library (i.e. the first declaration after the library declaration and any usings, includes, code systems, value sets, codes, concepts, and parameters).
3. If not specified, the context is determined by
* The default context, as specified by the first using declaration
* The `unfiltered` context, indicating that expressions in the library are not expressed from the perspective of a particular context

For more information, see the [Retrieve Context](https://cql.hl7.org/02-authorsguide.html#retrieve-context) discussion in the CQL specification.

### Code Systems
{: #code-systems}

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