xpath fn:replace says Extension functions must have a prefix

[jangid]

When I use xpath replace like this

<xsl:value-of select="replace('Hello World', 'l', 'z')"/>

it says:
Extension functions must have a prefix

[uogbuji]

Sorry about the delay. I need to set up better notifications. The code didn't show up properly. Did you use ``` to wrap it (according to GitHub Flavored Markdown)?