Reference

An XPath expression uses a namespace prefix that is not declared in the stylesheet. Declaring the prefix on xsl:stylesheet fixes it.

A type error: an expression returned a sequence or type that does not match what the function, operator or comparison expects. The strict type rules of XPath 2.0+ are usually behind it.

Two xsl:result-document instructions resolved to the same output URI — usually a static href inside a loop. Make the href dynamic.

Not a processor bug: an xsl:message with terminate="yes" fired. The stylesheet stopped itself — read the message text to see why.

Two or more templates match the same node with equal priority. Saxon warns (or errors in strict mode) and picks the last one declared — make the intent explicit.

An XSLT element appears somewhere the language grammar does not allow: wrong nesting, wrong order, or content at the stylesheet top level that must live inside a template.

Two xsl:variable or xsl:param declarations with the same name exist at the same level — often caused by a stylesheet being included twice.

Returns the value of a named accumulator computed after processing the current node in streaming mode.

Returns the value of a named accumulator computed before processing the current node in streaming mode.

Returns a new array containing only the members for which a predicate function returns true.