---
type: "fhir-fhirpath-function"
title: "FHIR FHIRPath Function: checkModifiers"
source: "source/fhirpath.html"
---

# FHIR FHIRPath Function: checkModifiers

This page is part of **FHIR FHIRPath** (FHIR-specific extensions). Base spec lives at [FHIRPath](/fhirpath).

`checkModifiers(modifier : string) : collection`

For each element in the input collection, verifies that there are no modifying extensions defined other than the ones given by the `modifier` argument (comma-separated string). If the check passes, the input collection is returned. Otherwise, an error is thrown, including if modifier is empty.

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