The prefix for those methods are bound to different namespaces. The namespace indicates the category, purpose, and “owner”.
fnare the standard XQuery, XPath, and XSLT functions (in this namespace: http://www.w3.org/2005/xpath-functions). You can expect them to be available in any standard XQuery, XPath, and XSLT engine.
ctsfunctions are the MarkLogic Core Text Search built-in functions (in this namespace: http://marklogic.com/cts). They are a set of MarkLogic specific functions that are used for search and query operations.
xdmpfunctions are the MarkLogic XML Database Management Platform built-in functions (in this namespace: http://marklogic.com/xdmp). They are a set of MarkLogic custom functions that provide extra utility functions and MarkLogic database specific actions.
The full set of functions available in MarkLogic, broken out by category and namespace
- XQuery: https://docs.marklogic.com/all
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