XSLT, 2nd Edition

Name

[2.0] trace()

Outputs diagnostic messages useful in tracing the processing of a stylesheet.

Syntax

item()* trace($value as item()*, $label as xs:string)

Inputs

A sequence of items and an xs:string. The string is typically something such as The value of $x is:. A diagnostic message containing that string and the value of the items in the sequence can be very useful in tracing the processing of the stylesheet.

Outputs

The output of the trace() function is the input sequence of items. They are returned without changes.

In addition, trace() converts the sequence of items into an xs:string. That string and the second argument are typically combined into a diagnostic message. Almost all of the details of the trace() function are implementation-dependent. The format of the diagnostic message, the destination of the diagnostic message, and the order in which calls to the trace() function are evaluated can vary from one processor to the next.

Defined in

XQuery 1.0 and XPath 2.0 Functions and Operators section 4, “The Trace Function.”

Example

This stylesheet is a smaller version of the stylesheet we used to illustrate the data() function. We want to create trace messages each time we invoke the datatest:print-item() function we created. Here’s the stylesheet:

<?xml version="1.0"?>
<!-- trace.xsl --> <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:datatest="http://www.oreilly.com"> <xsl:output method="text"/> <xsl:template ...