This test should not raise XD0008, because variable $value need not be evaluated.

The constant string "concat('test-',$value)" is passed to string-replace,  This step then interprets the string as an XPath expression according to the section 2.6.2.2 Step XPath Context, which states that the set of in-scope variables is "None, unless otherwise specified by the step", thus 

The source port of p:string-replace does not admit sequences, and the input to this test is a sequence of three documents.  Therefore, this test should expect XD0006.


<p:declare-step version="1.0" xmlns:p="http://www.w3.org/ns/xproc">
                <p:input port="source" sequence="true" />
                <p:output port="result" sequence="true" />

                <p:variable name="value" select="/doc/a" />

                <p:string-replace match="//doc" replace="concat('test-',$value)"
 />

    </p:declare-step>