Xquery err:XPST0017 Function parse-json()

Question

I tried to use the following function in an XQuery in eXide from eXist-db:

 let $x := parse-json(substring-before(substring-after($body,'('),');'))

but it gives me the following error:

err:XPST0017 Function parse-json() is not defined in module namespace: http://www.w3.org/2005/xpath-functions