Module functions 

XPath 1.0 Core Function Library (§25).

Implements all XPath 1.0 core functions as specified in §4 of the XPath 1.0 Recommendation.

UPSTREAM-PARITY

All functions follow the XPath 1.0 specification and libxml2 observable behavior, including edge cases and historical quirks.

Courts

XPATH-FUNCTIONS-*

Upstream contract

Mirrors the core-function library of upstream xpath.c (SRC-LIBXML2-2.15.0-XPATH-C, parity target libxml2 2.15.3 oracle): the 25 XPath 1.0 §4 functions (node-set, string, boolean, number groups) with libxml2 observable edge cases.

Conceptual behavior

Implements each function over already-evaluated XPathValue arguments with the upstream argument-count and coercion behavior: node-set functions (last, position, count, id, local-name, namespace-uri, name), string functions (string, concat, starts-with, substring, translate, …), boolean functions and number functions (number, sum, floor, ceiling, round). number()/string() route through the R-000166 number formatter (1e9/1e-5 scientific threshold, DBL_DIG=15 fraction digits).

Ownership & safety invariants

Functions return owned XPathValues; node-set arguments are borrowed views over the tree (valid for the call). No function stores or caches argument pointers — values are copied at the boundary, so the registry is safe to share.

Historical quirks & epochs

R-000114 (attribute string-value must be the attribute content, not empty) and R-000166 (full double-precision value-of printing) were fixed against the 2.15.3 oracle; the number() corpus (967/967 cases) locks the formatting epoch. The E-008 stable libxslt epoch means any function-level divergence is a candidate bug, not an epoch difference.

Deliberate oddities

round()/floor()/ceiling() reproduce libxml2 IEEE-754 handling (including negative zero and NaN propagation) rather than Rust rounding helpers, which differ on ties and sign.

Proving courts

XPATH-FUNCTIONS-* differential probes and the 967/967 number() corpus compare results byte-identical against the oracle; the XSLT courts (CLI-XSLTPROC-0014/0015/0017) exercise value-of/format-number through these functions.

Tempting simplifications that would break parity

Do not delegate number formatting to Rust float formatting: the scientific threshold, digit counts and exponent padding are oracle-observable (R-000166). Do not coerce arguments more eagerly than upstream (e.g. empty node-sets to string) — R-000114 proved the string-value rules are observable.

Statics

CORE_FUNCTION_SLICE

The XPath 1.0 core function library, as a static (name, fn) slice.

Functions

core_functions

The XPath 1.0 core function library as a name→fn map.

lookup_core_function

Look up a core XPath 1.0 built-in by name (allocation-free; the table is built once and shared across every context).

Type Aliases

XPathFunction

Type alias for XPath functions.