Limitations on Index Path Expressions
You can only use subset of XPath for defining path range indexes. The limitations are described in Path Field and Path-Based Range Index Configuration in the XQuery and XSLT Reference Guide.
Note
Avoid creating multiple path indexes that end with the same element/attribute, as ingestion performance degrades with the number of path indexes that end in common element/attributes.
You can use cts:valid-index-path to test whether or not you can use an XPath expression to define a path range index. For details, see Testing the Validity of an Index Path Expression.
Note numbers, booleans, and nulls in JSON documents are indexed separately rather than all being treated as text. For details on constructing XPath expressions on JSON documents, see Traversing JSON Documents Using XPat in the Application Developer’s Guide.