libyang is not able to parse generic extensions defined in YANG schema. The currently supported extensions are only
All other extension definitions/instances are currently ignored and only warning Not supported "<name>" extension statement found, ignoring. is printed.
libyang uses its own XPath implementation to evaluate XPath expressions. The implementation completely lacks support for axes. Nevertheless, it should always be possible to write equivalent expressions without the use of axes.
If there are any XPath expressions defined as part of a deviation, they include literals, which are directly compared with identityref nodes (testing whether an identityref has a specific identity value), and the identity literal used is from the deviation module (meaning it could be written without a prefix), the prefix is mandatory for libyang to evaluate the XPath expression correctly.